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. Author manuscript; available in PMC: 2011 Aug 1.
Published in final edited form as: FEMS Microbiol Lett. 2010 May 14;309(1):55–61. doi: 10.1111/j.1574-6968.2010.02013.x

The Scl1 of M41-type group A Streptococcus binds the high-density lipoprotein

Yumin Gao 1,§,, Chunwei Liang 1,§, Ruidong Zhao 1, Slawomir Lukomski 2, Runlin Han 1,*
PMCID: PMC2906607  NIHMSID: NIHMS211836  PMID: 20528941

Abstract

Streptococcal collagen-like protein 1 (Scl1) is a virulence factor on the surface of group A Streptococcus (GAS). We have previously reported that several Scl1 proteins derived from various M-type GAS strains, including M41, can bind to low-density lipoprotein but Scl1 protein derived from M6-type GAS strain can not. Here, we demonstrated that recombinant protein, designated C176, derived from Scl1.41 of GAS M41-type strain also binds both plasma and purified high-density lipoprotein (HDL). Next, we determined that intact non-collagenous region of C176 was necessary and sufficient for HDL binding. C176-HDL interaction could be eliminated by the presence of low concentrations of the nonionic detergent, Tween 20, suggesting hydrophobic character of this interaction. We finally showed that whole GAS cells expressing native Scl1.41 protein absorbed HDL from human plasma in the absence of Tween 20 but M6-type GAS cells did not. Altogether, our results add further evidence to the importance of GAS-lipoprotein binding.

Keywords: High-density lipoprotein, streptococcal collagen-like protein, group A Streptococcus

Introduction

As an important species of Gram-positive bacterial pathogens, Streptococcus pyogenes (Group A Streptococcus, GAS) is responsible for a number of suppurative infections including pharyngitis, impetigo/pyoderma, erysipelas, cellulitis, necrotizing fasciitis, toxic streptococcal syndrome, and scarlet fever, as well as nonsuppurative sequelae including acute rheumatic fever, acute glomerulonephritis (Cunningham, 2000). Major virulence factors of GAS include lipoteichoic acid, the surface exposed M protein, hyaluronic acid capsule, as well as several other cell surface proteins that include the streptococcal collagen-like surface protein 1 (Scl1) (Lukomski, et al., 2000, Rasmussen, et al., 2000). Based on the surface M protein, GAS is serologically separated into over 100 M protein serotypes (Beall, et al., 1996).

Since two cell-surface streptococcal collagen-like proteins, Scl1 and Scl2 (also known as SclA and SclB) were identified in 2000 (Lukomski, et al., 2000, Rasmussen, et al., 2000), their structure and functions have been extensively studied. (Lukomski, et al., 2000, Rasmussen, et al., 2000, Lukomski, et al., 2001, Rasmussen & Bjorck, 2001, Whatmore, 2001, Humtsoe, et al., 2005, Han, et al., 2006, Han, et al., 2006, Pahlman, et al., 2007, Caswell, et al., 2008). Mature Scl1 proteins are demonstrated to contain the N-terminal noncollagenous variable (V) regions, the adjacent collagen-like (CL) regions, linker (L) regions and cell-wall/membrane (WM) regions. Scl2 proteins are similar to Scl1 in structure, but they lack the linker regions (Lukomski, et al., 2000). Both Scl1 and Scl2 share common ‘lollipop-like’ structure with stalks made of the CL regions and globular heads made of the V regions. CL regions are of disparate lengths and vary in Gly–Xaa–Yaa (GXY) repeat content (Han, et al., 2006). It has been reported that Scl1 proteins from some GAS serotypes can interact with apolipoprotein B-containing lipoproteins, mainly low density lipoprotein (LDL) in human plasma (Han, et al., 2006). The V regions of recombinant Scl1 (rScl1) derived from M1, M12, M28 and M41 serotypes, but not those of recombinant Scl2 (rScl2) from M4, M77, M28 serotypes, can bind to both purified ApoB100 and plasma LDL. However, the physiological and pathological significances of the interaction remain to be elucidated.

HDL, one of major lipoproteins, enables lipids like cholesterol and triglycerides to be reversely transported. A high level of HDL-associated cholesterol seems to protect against cardiovascular diseases (Kapur, et al., 2008). It has also been demonstrated that HDL may participate in innate immunity by protecting against some infections (Grunfeld & Feingold, 2008). When infection and inflammation induce the acute-phase response, the level of HDL in plasma is decreased (Khovidhunkit, et al., 2004). HDL can bind endotoxin (lipopolysaccharide, LPS) of Gram-negative bacteria and lipoteichoic acid (LTA) of Gram-positive bacteria, and neutralize their toxic effects (Grunfeld, et al., 1999, Khovidhunkit, et al., 2004). In addition, HDL possesses a broad antiviral activity (Singh, et al., 1999). Notably, trypanosoma lytic factors (TLF), one subsets of HDL, prevents human from Trypanosoma brucei (Raper, et al., 2001) and Leishmania infections (Samanovic, et al., 2009). Interestingly, serum opacity factor (SOF) expressed by class II GAS strains interacts with ApoAI and ApoAII of HDL subsequently causing the disrupture of HDL, and which may attenuate anti-inflammatory functions of HDL and contribute to the pathogenesis of GAS infection (Courtney, et al., 2006).

The present study demonstrates that Scl1 from M41-type GAS ATCC12373 specifically binds HDL. The interaction mechanism was also studied.

Material and methods

Bacterial cultures

Two strains of group A Streptococcus, M6 (CMCC32175, obtained from China Medical Culture Collection Center) and M41 (ATCC12373, obtained from American Type Culture Collection), were employed in this study. Cultivation of GAS was performed as previous report (Han, et al., 2006). The GAS was grown in Todd-Hewitt broth (Becton and Dickinson company, MD) supplemented with 0.2% Yeast extract (OXOID, Hampshire, England) (THY medium). Nutrient broth agar containing 5% sheep blood was used as solid medium. GAS was incubated in THY broth, 5% CO2, 37°C to mid-logarithmic phase (OD600nm ~ 0.5). GAS cell was collected by centrifugation at 6000 g for 10min at 4 °C, and cell pellet was washed twice with PBSA (PBS containing 0.02% NaN3), and the GAS cell suspensions in PBSA were used for the following experiments. Escherichia coli was grown at 37°C in Luria-Bertani (LB) broth, (Tryptone 10 g L−1, Yeast extract 5 g L−1 (OXOID), and LB agar was used as a solid medium. 100 μg−1 ml ampicillin (Bio Basic Inc, Ontario, Canada) and 0.2 μg ml−1 anhydrotetracycline (IBA-GmbH, Gottingen, Germany) were used for selection markers.

Recombinant proteins

Recombinant streptococcal collagen-like proteins (rScl) were produced in E. coli using the Strep-tag II expression and purification system (IBA-GmbH), as described previously (Xu, et al., 2002, Han, et al., 2006). Briefly, DNA fragments encoding the extracellular portions of Scl1 were extracted from ATCC12373. The target DNAs were amplified by PCR, digested with BsaI, and cloned into the vector pASK-IBA2, designed for periplasmic expression. E. coli BL21 strains-harboring plasmid constructs were grown in the presence of ampicillin and protein expression was induced during the exponential growth with anhydrotetracycline for 3 h. Recombinant proteins were extracted from the periplasm by FastBreak Cell Lysis Reagent (Promega, WI) and were purified by affinity chromatography with Strep-Tactin Sepharose. Three different rScl1 proteins (C176, C176V and C176T) (Table 1), all derived from Scl1.41 variant were constructed. rScl1s also contained a short affinity Strep-tag II (WSHPQFEK) at the C-terminus, which binds to Strep-Tactin Sepharose.

Table 1.

Strains, plasmids, recombinant proteins and primers used in the present study.

Strains, plasmids or recombinant protein Source or application
Strains Souce
 ATCC12373 ATCC
 E. coli BL21 Shanghai Sangon
Plasmids
 pASK-IBA2 IBA-GmbH
Recombinant proteins
 C176 This work
 C176V This work
 C176T This work
Primers Amplification
 C176F: 5′-atggtaggtctcaggccgatatctgggaccaggagcaaag-3′ C176 and C176V
 C176R: 5′-atggtaggtctcagcgctttgttcgcctggttgctctggc-3′ C176 and C176T
 C176VR: 5′-atggtaggtctcagcgctacgtaaagcatcgctcttaagacc-3′ C176V
 C176TF: 5′-atggtaggtctcaggccagttatgatagcgtagaactttataat-3′ C176T
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Affinity chromatography-binding assay

Affinity-chromatography columns were packed with 0.15 ml of the Strep-Tactin-Sepharose resin (50% suspension) (IBA-GmbH) and equilibrated with buffer W (100 mM Tris-HCl pH 8.0, 1 mM EDTA, 150 mM NaCl). 50 μg of each purified rScl protein was applied onto the column to allow binding through C-terminal affinity tags. After washing with 8 column volumes (8 CV) of buffer W 0.5 ml of human HDL (0.1 mg ml−1) (Calbiochem, Darmstadt, Germany) were passed over rScl1-bound or over the non-rScl1 bound control columns. In some experiments, a 0.5ml of human plasma was applied to each column. Plasma obtained from healthy volunteers in accordance with Inner Mongolia Agriculture University regulations was applied to the columns. Columns were washed with 8 CV of buffer W. In some experiments, buffer W containing 0.05% Tween 20 was employed. Complexes of rScl1 proteins and their ligands were eluted in 0.15 ml fractions with 4 CV of buffer E (100 mM Tris-HCl pH 8.0, 1.0 mM EDTA, 150 mM NaCl and 25 mM desthobiotin). Total protein presented in each sample was precipitated with 10% trichloroacetic acid (TCA) for 1 h on ice. Following centrifugation (13000g, 10 min), the pellets were resuspended in 1 M Tris-HCl pH 8.0 buffer and analyzed by both SDS-PAGE stained with RAPIDstain (Geno Technology) and Immunoblotting. Immunodetection of ApoAI was performed with a goat anti-ApoAI antibody (Cliniqa, CA) followed by HRP conjugated donkey anti-goat secondary antibody (R&D Systems, MN). Immunodetection of Strep-Tag was performed with HRP conjugated Strep-Tactin (IBA-GmbH). The detection was performed with chemiluminescence reagent (Tiangen, Beijing).

Enzyme-linked immunosorbent assay

A 100 μl of 2 μM rScl1 was coated onto microplate wells (Grierner bio-one, Frickenhausen, Germany) at room temperature for 2 h. Following washes with TBS (Tris-buffered saline) or TBST (TBS-0.05% Tween 20), 100μl of 0.5 μg HDL in TBS or TBST was added into the wells and incubated at room temperature for 1.5 h. After three washes with TBS or TBST 100μl of diluted goat polyclonal anti-ApoAI antibody was added to the corresponding wells and incubated for 1.5 h. HRP-conjugated donkey anti-goat was used as secondary antibody and the reaction was developed with TMB substrate (Tiangen). After 15 min of color development, the stop solution (8.5 M acetic acid, 2.5 M H2SO4) was added and the absorbance was recorded at 450 nm.

Whole cell binding assays

The binding of HDL to the GAS (Type M6 and M41) was tested using GAS cells which were either immobilized onto microplate wells or were in suspension. GAS cell suspensions were added to microplate wells and incubated at room temperature for 1.5 h. Wells were washed and blocked overnight with 200 μl of 1% BSA in TBS or TBST at 4°C. HDL binding was performed as described above in the rScl1 binding ELISA. For the HDL binding to GAS cells in suspension, cells were incubated for 1.5 h with 1% BSA in TBS or TBST. After washing with TBS or TBST 100μl of human plasma was added to 1 ml of the cells. Following a 1 h incubation at room temperature, bacterial cells were pelleted and washed three times with TBS or TBST. After the final centrifugation, cell-bound proteins were dissociated from the cells by the incubation with 200 μl of 0.1 M glycine-HCl solution pH 2 for15 min. Bacterial cells were then removed by centrifugation and the proteins in the supernatant were precipitated with10% TCA, and analyzed by SDS-PAGE and immunoblotting. Electroblotting was carried out with a constant voltage of 30V for 1h to transfer ApoAI and with a constant current of 300mA for 3h to transfer ApoB100. The immunodetection of ApoAI was performed with a goat anti-ApoAI antibody, followed by HRP-conjugated donkey anti-goat secondary antibody as described above. The presence of ApoB100 was tested with a goat anti-LDL antibody (Chemicon, CA) followed by HRP-conjugated donkey anti-goat antibody (R&D Systems), and the detection was performed with chemiluminescence reagent (Tiangen, Beijing).

Statistical analysis

Results were expressed as mean±SD. Statistical significance was calculated using two-tailed Student's t-test for comparisons of two groups and Student-Neuman-Keuls for comparison of multiple groups, respectively.

Results

Recombinant Scl1.41 protein binds human plasma HDL via noncollagenous region

It was previously reported that several Scl1 proteins interact with LDL/ApoB100 via globular noncollagenous V regions (Han, et al., 2006). Here, we are testing the hypothesis that Scl1.41 variant possess binding ability to HDL. Recombinant Scl1 (rScl1) proteins C176, C176V, and C176T were constructed that are derived from Scl1.41 protein of GAS M41-type strain ATCC 12373. PCR-amplified DNA fragments corresponding to a full-length or partial scl1.41-gene sequence were cloned, expressed, and purified in E. coli BL21 (Table 1; Fig.1a). rScl1 proteins were immobilized onto Strep-Tactin columns through their C-terminal tags (strep-tag II) and these affinity columns were used to detect Scl1 ligands in human plasma. 0.5 ml of human plasma was applied to these columns, including the control column without rScl1 protein. Eluted samples containing presumed C176-ligand complexes were analyzed by 15% SDS-PAGE and Western immunoblotting.

Fig. 1.

Fig. 1

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Interactions of recombinant Scl1 constructs with human plasma HDL. Human plasma was applied to affinity columns containing immobilized rScl1 constructs C176, C176V, and C176T or to a control column without rScl protein. Protein complexes eluted from the columns were precipitated with TCA. (a) Schematic representation of rScl1 constructs (not to scale). V, variable region; CL, collagen-like region; L, linker region. (b) SDS-PAGE analysis. Eluted fractions from columns were analyzed by 15% SDS-PAGE stained with RAPIDstain. HDL preparations were used as marker. rScl constructs were marked with solid triangles. Common ~25-kDa band is marked with open triangles. (c) Western blot analysis. Proteins shown in (a) were transfered onto a nitrocellulose membrane. Presence of ApoAI was tested with anti-ApoAI antibody (upper panel) and rScl1 were detected with a Strep-Tactin-HRP conjugate (bottom panel). Immunoreactivity was visualized using chemiluminescence substrate.

SDS-PAGE analysis of a sample obtained from the column immobilized with the full-length construct C176 revealed the presence of the 25-kDa band that co-migrated with a protein present in HDL marker (Fig. 1b). In addition, a similar protein-band was present in sample eluted from the column immobilized with C176V, containing the entire noncollagenous V region of Scl1, but not with truncated construct C176T. This protein was absent in no rScl1 control. In order to verify that 25-kDa protein was ApoA I, the same samples were blotted onto a membrane and immunoreacted with specific anti-ApoA I antibodies (Fig. 1c). As expected, the 25-kDa band found in C176 and C176V samples was identified as ApoA I.

To confirm the ligand-binding ability of C176 derivatives that were detected using human plasma we used the same affinity-chromatography columns with purified HDL. The samples eluted from the columns with immobilized rScl1 or PBS were analyzed by 15% SDS-PAGE and Western immunoblotting (Fig. 2). The 25-kDa band of ApoAI contained in HDL was detected in C176 sample by staining and with anti-ApoAI antibody, but not in a sample eluted from the control column without rScl1 protein. The N-terminal 42-aa-truncated variant of C176 (C176T) was not able to bind to HDL. On the contrary, the recombinant C176V, which contains all 84 amino acids of the V region but lacks the CL region, could bind HDL implying that the V region was responsible for the binding. Altogether, our results identified HDL as a new ligand for Scl1.41 protein. The binding occurs via a noncollagenous domain of Scl1, which is necessary and sufficient for HDL binding.

Fig. 2.

Fig. 2

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Interactions of recombinant Scl1 constructs with purified HDL. Commercial HDL was applied to affinity columns containing immobilized rScl1 constructs C176, C176V, and C176T or to control column without rScl1 protein. Protein complexes eluted from the columns were TCA-precipitated. Protein samples eluted from columns were analyzed by 15% SDS-PAGE stained with RAPIDstain (upper panel). HDL preparations were used as marker. The rScl1s were marked with solid triangles. Common ~25-kDa band was identified as ApoAI (open triangles). Proteins shown in upper panel were transferred onto a nitrocellulose membrane. Presence of ApoAI was tested with anti-ApoAI antibody. Immunoreactivity was visualized using chemiluminescence substrate (bottom panel).

Characterization of rScl1-HDL binding

In contrast to P176-LDL binding (Han, et al., 2006), the binding between C176 and HDL could not be detected by traditional ELISA. We hypothesized that the presence of a nonionic detergent, Tween 20, in the wash buffer affected C176-HDL binding. To test this hypothesis, the binding experiments employing both affinity chromatography and ELISA were performed with or without Tween 20 (Fig. 3).

Fig. 3.

Fig. 3

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Effect of Tween 20 on C176 binding to HDL. (a) Affinity chromatography analysis. Affinity chromatography columns immobilized with rScl constructs and exposed to HDL were washed with and without Tween 20-containing buffers. Eluted samples were analyzed by 15% SDS-PAGE. rScl1s are marked with solid triangle and ApoAI is marked with open triangle. (b) Detection of HDL and rScl1 constructs by dot immunoblotting. Protein samples shown in A were spotted onto a nitrocellulose membrane. Presence of ApoAI was tested with anti-ApoAI antibody (bottom row) and rScl1s were detected with a Strep-Tactin-HRP conjugate (upper row). Immunoreactivity was visualized using chemiluminescence substrate. (c) Tween 20 inhibits the interaction of C176V with HDL by ELISA. Different concentrations of C176V were immobilized onto microplate wells and 0.5 μg of HDL was added to the wells. Wells were washed with buffer containing (TBST) or lacking Tween 20 (TBS). Bound HDL was detected with the anti-ApoAI antibody and the secondary antibody conjugated to HRP. The color was developed with an HRP substrate and absorbance was recorded at 450nm. Mean absorbance values±SD from triplicate wells were obtained after subtracting the OD values of the control wells without C176V.

In affinity chromatography analysis, the HDL-binding positive constructs C176 and C176V were immobilized onto duplicate columns with Strep-Tactin Sepharose, and purified HDL was passed over the columns. Columns were washed using buffer W with or without 0.05% Tween 20. The eluted samples obtained from affinity chromatography columns treated with Tween 20 did not contain HDL, whereas those without Tween 20 did (Fig. 3a and 3b). These data were further confirmed by ELISA (Fig. 3c). Microplate wells were immobilized with different concentrations of C176V and incubated with purified HDL. Wells were washed with buffer containing (TBST) or lacking (TBS) Tween 20 and bound HDL was detected with anti-ApoAI antibody. The C176V protein was able to bind to HDL in a concentration-dependent manner, indicating that binding was specific, but only when washing was done with TBS. No HDL binding to C176 was detected under the same experimental conditions except for washing with TBST (OD values recorded were negative), These experiments fully support our previous results indicating that rScl1.41-HDL interaction is specific but different from that between rScl1 and LDL, which is not inhibited by the presence of low detergent concentrations.

High-density lipoprotein binds to Scl1.41 protein on GAS surface

To study HDL binding by GAS cells, M41-type ATCC12373 strain [Its scl1.41 allele is identical to CMCC32198 (Gene bank accession number EU915249)] and M6-type CMCC32175 strain [Its scl1.6 allele is identical to M6-type MGAS6169 strain (Gene bank accession number EU127997)] were used. In an ELISA based assay, GAS cells were immobilized into microplate wells and incubated with HDL. Following incubation, duplicated wells (each in triplicate) were washed with TBS or TBST to test whether Tween 20 inhibits the binding of HDL to GAS cells (Fig. 4a). As we reported above for C176-HDL, HDL binding to whole M41-type GAS cells was only detected when samples were washed with a Tween 20-free buffer. However, M6-type GAS cells did not bind to HDL with or without Tween 20 in wash buffer.

Fig. 4.

Fig. 4

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HDL binding to GAS cells. (a) HDL binding to GAS cells by ELISA. GAS cells were immobilized onto microplate wells and incubated with HDL. Wells were washed with buffer containing or lacking Tween 20. Bound HDL was detected with anti-HDL-specific antibody followed by HRP-conjugated secondary antibody and the HRP-substrate reaction was measured spectrophotometrically at 450 nm. Average absorbance value±SD from triplicate wells were obtained after subtracting the OD values of the control wells without HDL. (b) HDL binding to GAS cells in suspension. GAS cells were incubated with 1% BSA for 1.5 h. After washing cells were mixed with human plasma. Cells with adsorbed proteins were washed with TBS or TBST. Surface-bound proteins were then dissociated from the cells with glycine-HCl buffer (pH 2.0) and TCA-precipitated. Detections of ApoAI and ApoB100 were carried out by immunoblotting using goat anti-ApoAI antibody and goat anti-LDL antibody, respectively.

Scl1-specific absorption of plasma HDL to GAS cells was next determined in liquid phase (Fig. 4b). GAS cells were incubated with human plasma for 1 h and unbound proteins were removed by washing the cells with PBS or PBST. GAS cell-associated HDL was detected by Western blot analysis with the polyclonal antibody to ApoAI. The results showed that Tween 20 displaced HDL from M41-type GAS cells since only traced amounts of bound HDL was detected following washes with TBST. However, the only weak interaction between M6-type GAS cells and HDL was observed either in the presence or in the absence of Tween 20 in wash buffer. Therefore, HDL-GAS interaction may be specifically mediated by Scl1. In addition, the LDL binding to M41-type GAS cells was not affected by Tween 20 further implying different characteristics of interactions with both lipoprotein ligands.

Discussion

The cumulative evidence suggests a complex interplay between plasma lipoproteins (PLPs) and infections (Khovidhunkit, et al., 2004). We recently postulate that PLPs might be important components of the host defense system (Han, 2009). Our research may be an important addition to this field.

Through its surface protein, GAS interacts with the host molecules in plasma, lymphatic system, skin and soft tissue (Courtney, et al., 2002). It was for the first time demonstrated that rScl1, C176, could bind to purified and plasma HDL. The results might be an important addition to the interaction of lipoprotein with pathogenic bacteria. In current study, we used M6-type CMCC32175 strain as a negative control since M6-type MGAS6169 strain does not bind to plasma lipoproteins (Caswell, et al., 2008). Therefore, HDL may specifically interact with Scl1 of M41-type ATCC12373 strain. Interestingly, serum opacity factor expressed by class II GAS can disrupt HDL, which implies HDL may play an important role in protecting against GAS infection. M41 ATCC12373 falls into Class I GAS (Rakonjac, et al., 1995). M41-type GAS-bound HDL might not be disrupted since there is no serum opacity factor expressed in this strain. Therefore, HDL might be a foe to GAS. However, the protecting mechanism remains to be elusive.

C176 via its V region could also interact with LDL whereas C176T (Partial V region-truncated variant) still bound to LDL (Data no shown) but did not bind HDL. These results suggest that the sites on Scl1 for the binding to HDL and LDL may be different. Additionally, C176 could be used for the production of lipid-free serum since it can specifically absorb both LDL and HDL from plasma or serum.

ApoAI and ApoAII are major apolipoproteins in HDL. In order to explore the sites of HDL interacting with rScl1, affinity chromatography assays were used to examine the interaction between C176 and purified recombinant ApoAI, ApoAII. However, C176 could bind to neither ApoAI nor ApoAII (Data not shown). Purified ApoAI and ApoAII may have different conformation from that of natural ApoAI and ApoAII in HDL complex, so the possibility that C176 can bind to HDL via ApoAI and ApoAII can not be excluded completely.

In summary, the V region of Scl1 derived from M41-type GAS could bind to purified and plasma HDL, and this binding may be mediated by hydrophobic interaction. The HDL-Scl1 interaction may play an important role in protecting against GAS infection.

Acknowledgments

We thank Y. Pang, S. Du, L. M. Li and F. Huo for technical assistance. This work was supported by the start-up Grant K32615 from the Inner Mongolia Agricultural University (to R. Han) and in part by National Institutes of Health Grant AI50666 (to S. Lukomski).

References

  1. Beall B, Facklam R, Thompson T. Sequencing emm-specific PCR products for routine and accurate typing of group A streptococci. J Clin Microbiol. 1996;34:953–958. doi: 10.1128/jcm.34.4.953-958.1996. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Caswell CC, Han R, Hovis KM, Ciborowski P, Keene DR, Marconi RT, Lukomski S. The Scl1 protein of M6-type group A Streptococcus binds the human complement regulatory protein, factor H, and inhibits the alternative pathway of complement. Mol Microbiol. 2008;67:584–596. doi: 10.1111/j.1365-2958.2007.06067.x. [DOI] [PubMed] [Google Scholar]
  3. Courtney HS, Hasty DL, Dale JB. Molecular mechanisms of adhesion, colonization, and invasion of group A streptococci. Ann Med. 2002;34:77–87. doi: 10.1080/07853890252953464. [DOI] [PubMed] [Google Scholar]
  4. Courtney HS, Zhang YM, Frank MW, Rock CO. Serum opacity factor, a streptococcal virulence factor that binds to apolipoproteins A-I and A-II and disrupts high density lipoprotein structure. J Biol Chem. 2006;281:5515–5521. doi: 10.1074/jbc.M512538200. [DOI] [PubMed] [Google Scholar]
  5. Cunningham MW. Pathogenesis of group A streptococcal infections. Clin Microbiol Rev. 2000;13:470–511. doi: 10.1128/cmr.13.3.470-511.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Grunfeld C, Feingold KR. HDL and innate immunity: a tale of two apolipoproteins. J Lipid Res. 2008;49:1605–1606. doi: 10.1194/jlr.E800011-JLR200. [DOI] [PubMed] [Google Scholar]
  7. Grunfeld C, Marshall M, Shigenaga JK, Moser AH, Tobias P, Feingold KR. Lipoproteins inhibit macrophage activation by lipoteichoic acid. J Lipid Res. 1999;40:245–252. [PubMed] [Google Scholar]
  8. Han R. Plasma lipoproteins are important components of the host defense system? Journal of Immunology. 2009;182:134–174. [Google Scholar]
  9. Han R, Caswell CC, Lukomska E, et al. Binding of the low-density lipoprotein by streptococcal collagen-like protein Scl1 of Streptococcus pyogenes. Mol Microbiol. 2006;61:351–367. doi: 10.1111/j.1365-2958.2006.05237.x. [DOI] [PubMed] [Google Scholar]
  10. Han R, Zwiefka A, Caswell CC, et al. Assessment of prokaryotic collagen-like sequences derived from streptococcal Scl1 and Scl2 proteins as a source of recombinant GXY polymers. Appl Microbiol Biotechnol. 2006;72:109–115. doi: 10.1007/s00253-006-0387-5. [DOI] [PubMed] [Google Scholar]
  11. Humtsoe JO, Kim JK, Xu Y, Keene DR, Hook M, Lukomski S, Wary KK. A streptococcal collagen-like protein interacts with the alpha2beta1 integrin and induces intracellular signaling. J Biol Chem. 2005;280:13848–13857. doi: 10.1074/jbc.M410605200. [DOI] [PubMed] [Google Scholar]
  12. Kapur NK, Ashen D, Blumenthal RS. High density lipoprotein cholesterol: an evolving target of therapy in the management of cardiovascular disease. Vasc Health Risk Manag. 2008;4:39–57. doi: 10.2147/vhrm.2008.04.01.39. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Khovidhunkit W, Kim MS, Memon RA, Shigenaga JK, Moser AH, Feingold KR, Grunfeld C. Effects of infection and inflammation on lipid and lipoprotein metabolism: mechanisms and consequences to the host. J Lipid Res. 2004;45:1169–1196. doi: 10.1194/jlr.R300019-JLR200. [DOI] [PubMed] [Google Scholar]
  14. Lukomski S, Nakashima K, Abdi I, Cipriano VJ, Shelvin BJ, Graviss EA, Musser JM. Identification and characterization of a second extracellular collagen-like protein made by group A Streptococcus: control of production at the level of translation. Infect Immun. 2001;69:1729–1738. doi: 10.1128/IAI.69.3.1729-1738.2001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Lukomski S, Nakashima K, Abdi I, et al. Identification and characterization of the scl gene encoding a group A Streptococcus extracellular protein virulence factor with similarity to human collagen. Infect Immun. 2000;68:6542–6553. doi: 10.1128/iai.68.12.6542-6553.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Pahlman LI, Marx PF, Morgelin M, Lukomski S, Meijers JC, Herwald H. Thrombin-activatable fibrinolysis inhibitor binds to Streptococcus pyogenes by interacting with collagen-like proteins A and B. J Biol Chem. 2007;282:24873–24881. doi: 10.1074/jbc.M610015200. [DOI] [PubMed] [Google Scholar]
  17. Rakonjac JV, Robbins JC, Fischetti VA. DNA sequence of the serum opacity factor of group A streptococci: identification of a fibronectin-binding repeat domain. Infect Immun. 1995;63:622–631. doi: 10.1128/iai.63.2.622-631.1995. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Raper J, Portela MP, Lugli E, Frevert U, Tomlinson S. Trypanosome lytic factors: novel mediators of human innate immunity. Curr Opin Microbiol. 2001;4:402–408. doi: 10.1016/s1369-5274(00)00226-5. [DOI] [PubMed] [Google Scholar]
  19. Rasmussen M, Bjorck L. Unique regulation of SclB - a novel collagen-like surface protein of Streptococcus pyogenes. Mol Microbiol. 2001;40:1427–1438. doi: 10.1046/j.1365-2958.2001.02493.x. [DOI] [PubMed] [Google Scholar]
  20. Rasmussen M, Eden A, Bjorck L. SclA, a novel collagen-like surface protein of Streptococcus pyogenes. Infect Immun. 2000;68:6370–6377. doi: 10.1128/iai.68.11.6370-6377.2000. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Samanovic M, Molina-Portela MP, Chessler AD, Burleigh BA, Raper J. Trypanosome lytic factor, an antimicrobial high-density lipoprotein, ameliorates Leishmania infection. PLoS Pathog. 2009;5:e1000276. doi: 10.1371/journal.ppat.1000276. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Singh IP, Chopra AK, Coppenhaver DH, Ananatharamaiah GM, Baron S. Lipoproteins account for part of the broad non-specific antiviral activity of human serum. Antiviral Res. 1999;42:211–218. doi: 10.1016/s0166-3542(99)00032-7. [DOI] [PubMed] [Google Scholar]
  23. Whatmore AM. Streptococcus pyogenes sclB encodes a putative hypervariable surface protein with a collagen-like repetitive structure. Microbiology. 2001;147:419–429. doi: 10.1099/00221287-147-2-419. [DOI] [PubMed] [Google Scholar]
  24. Xu Y, Keene DR, Bujnicki JM, Hook M, Lukomski S. Streptococcal Scl1 and Scl2 proteins form collagen-like triple helices. J Biol Chem. 2002;277:27312–27318. doi: 10.1074/jbc.M201163200. [DOI] [PubMed] [Google Scholar]

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