Table 1.
Transmembrane proteins localized to the plasma membrane identified by tandem mass spectrometry in human platelets and SAGE analysis in mouse megakaryocytes. Proteins are arranged according to families. Information is given on general function or specific function in platelets, where known. Several proteins are predominantly expressed on intracellular membranes and platelet α-granules and are translocated to the plasma membrane on activation. General information was obtained from NCBI, Swiss-Prot/TrEMBL and PubMed databases. The number of transmembrane domains (No. of predicted TMDs) in each protein was predicted with TMHMM v.2.0 (25). The highest number of unique peptides (No. of unique peptides) identified in a single mass spectrometry experiment are shown. The search algorithm (Mascot and/or Sequest) used to identify each protein is indicated, as is the method used to enrich transmembrane proteins (biotin/NA, biotinylation and NeutrAvidin affinity chromatography; FFE-IM, free flow electrophoresis-intracellular membrane fraction; FFE-PM, free flow electrophoresis-plasma membrane fraction; WGA, wheat germ agglutinin affinity chromatography). All proteins were identified by two or more peptide hits with at least one of the search algorithms. The number of SAGE tags (No. of SAGE tags) identified in mouse megakaryocytes is indicated in the final columns. Transcripts for 37 out of 44 proteins (84%) identified by MS/MS analysis of human platelets were identified in mouse megakaryocytes by SAGE. A question mark in the SAGE tag column indicates that the transcript could be present, but that there is currently not enough sequence information in the public databases for the identification of SAGE tags.
Family name (Protein name) | Swiss-Prot/TrEMBL accession | Function | No. of predicted TMDs | No. of unique peptides | Search algorithm | Enrichment | No. of SAGE tags |
---|---|---|---|---|---|---|---|
Cadherin superfamily | |||||||
protocadherin FAT 2 | Q9NYQ8 | Calcium-dependent cell-adhesion protein | 1 | 2 | Mascot | WGA, FFE-PM | ? |
Ig superfamily and associated proteins | |||||||
basigin | P35613 | Associates with carboxylate transporters; undergoes homophilic binding; function in platelets is not known | 2 | 3 | Sequest | WGA | 26 |
CD226 | Q15762 | Involved in intercellular adhesion and modulation of signaling; supports platelet adhesion to endothelial cells | 1 | 5 | Mascot, Sequest | biotin/NA, WGA | 3 |
CD84 | O15430 | Member of the SLAM family of homophilic adhesion receptors; stabilizes platelet-platelet interactions during thrombosis | 1 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 3 |
endothelial cell-selective adhesion molecule | Q96AP7 | Found at tight junctions in endothelial cells; function in platelets is not known | 1 | 3 | Mascot, Sequest | biotin/NA, FFE-PM | 9 |
FcR γ-chain | P30273 | Present as a complex with the collagen receptor, GPVI; the ITAM in the FcR γ-chain is critical for GPVI signaling | 1 | 2 | Mascot, Sequest | biotin/NA | 23 |
G6f | Q7Z5H2 | G6f gene is found within the MHC class III; interacts with Grb2 when phosphorylated; function in platelets is not known | 1 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 7 |
GPVI | Q9UIF2 | Major signaling receptor for collagen; present as a complex with FcR γ-chain | 1 | 3 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 6 |
MHC class I antigen (HLA-A) | Q8MHP8 | Presentation of antigens to the immune system | 1 | 6 | Mascot, Sequest | biotin/NA | 80 (total) |
MHC class I antigen B-52 | P30490 | Presentation of antigens to the immune system | 1 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 80 (total) |
MHC class I antigen Cw-15 | Q07000 | Presentation of antigens to the immune system | 1 | 8 | Mascot, Sequest | biotin/NA, FFE-PM | 80 (total) |
ICAM 2 | P13598 | Ligand for β2-integrins; function in platelets is not known | 1 | 3 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 2 |
JAM1 | Q9Y624 | Plays a role in tight junction formation and transmigration; function in platelets is not known | 1 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 5 |
JAM3 | Q9BX67 | May participate in cell-cell adhesion distinct from tight junctions; function in platelets is not known | 1 | 3 | Mascot, Sequest | biotin/NA, FFE-PM | 0 |
FcγRIIA | P12318 | Low affinity IgG receptor; mediates platelet activation by immune complexes via an ITAM regulated pathway | 1 | 2 | Mascot, Sequest | biotin/NA | Not in mouse |
PECAM-1 | P16284 | Major platelet receptor; undergoes homotypic binding; inhibits platelet activation by collagen and VWF | 1 | 12 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 7 |
TLT-1 | Q8IWY2 | Found on platelet α-granules and translocates on activation; contains an ITIM; supports late stage platelet activation | 1 | 2 | Mascot, Sequest | biotin/NA, FFE-IM | 13 |
Integrin family | |||||||
α2 integrin subunit | P17301 | α2β1 mediates platelet adhesion to collagen | 1 | 8 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 0 |
α6 integrin subunit | P23229 | α6β1 mediates platelet adhesion to laminin | 1 | 12 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 47 |
αIIb integrin subunit | P08514 | αIIbβ3 is the major platelet adhesion and aggregation receptor | 1 | 15 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 136 |
β1 integrin subunit | P05556 | associates with α2, α5 and α6 integrin subunits in platelets | 1 | 8 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 14 |
β3 integrin subunit | P05106 | associates with αIIb and αv integrin subunits in platelets | 1 | 17 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 41 |
Leucine-rich repeat family | |||||||
GPIX | P14770 | Subunit of the GPIb-IX-V complex that binds VWF | 1 | 5 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 11 |
GPV | P40197 | Subunit of the GPIb-IX-V complex that binds VWF | 1 | 11 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 9 |
GPIbα | P07359 | Subunit of the GPIb-IX-V complex that binds VWF | 1 | 5 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 21 |
GPIbβ | P13224 | Subunit of the GPIb-IX-V complex that binds VWF | 1 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 31 |
LRRC32 protein | Q14392 | Not known | 1 | 2 | Mascot, Sequest | biotin/NA | 0 |
Peptidase family | |||||||
ADAM 10 | O14672 | Proteolytic release of cell surface proteins, including TNFα and ephrin-A2; function in platelets is not known. | 1 | 5 | Mascot, Sequest | biotin/NA, FFE-PM | 11 |
ECE-1 | P42892 | Metabolism of big endothelin-1 to endothelin-1 | 1 | 2 | Mascot, Sequest | FFE-IM, WGA | 0 |
Protein tyrosine phosphatase family | |||||||
DEP-1 | Q12913 | Regulates contact inhibition of cell growth; function in platelets is not known | 1 | 11 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 1 |
Selectin family | |||||||
P-selectin | P16109 | Found on platelet α-granules and translocates on activation; mediates interaction with microparticles and leukocytes | 1 | 11 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 13 |
Steroid receptor family | |||||||
membrane associated progesterone receptor component 1 | O00264 | Receptor for progesterone; function in platelets is not known | 1 | 2 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 9 |
membrane associated progesterone receptor component 2 | O15173 | Receptor for progesterone; function in platelets is not known | 1 | 4 | Mascot, Sequest | FFE-IM, FFE-PM | 1 |
type I sigma receptor | Q99720 | Interacts with endogenous steroid hormones (progesterone and testosterone); function in platelets is not known | 1 | 2 | Mascot, Sequest | FFE-IM | 1 |
Tetraspanin family | |||||||
CD9 | P21926 | Major platelet tetraspanin; associates with platelet glycoproteins | 4 | 4 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 34 |
Tspan-9 | O75954 | Function in platelets is not known | 4 | 2 | Mascot, Sequest | biotin/NA, FFE-PM | 5 |
Tspan-33 | Q86UF1 | Function in platelets is not known | 4 | 3 | Mascot, Sequest | FFE-PM | 3 |
Tyrosine protein kinase family | |||||||
EphB1 | P54762 | Supports late stage aggregation via interaction with ephrin-B1 | 1 | 2 | Mascot, Sequest | biotin/NA | 0 |
Miscellaneous | |||||||
adipocyte plasma membrane-associated protein | Q9HDC9 | May play a role in adipocyte differentiation; function in platelets is not known | 1 | 3 | Mascot, Sequest | FFE-IM, FFE-PM | 2 |
BAT5 | O95870 | BAT5 gene is found within the MHC class III; function in platelets is not known | 2 | 2 | Mascot, Sequest | FFE-IM | 2 |
CD36 | P16671 | Putative receptor for collagen and thrombospondin in platelets | 2 | 5 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 0 |
CD92 | Q96KU3 | Probable choline transporter; function in platelets is not known | 9 | 2 | Sequest | FFE-PM | 5 |
sodium/potassium transporting, β 3 polypeptide | P54709 | Non-catalytic component of a Na+/K+-ATPase; responsible for establishing and maintaining resting membrane potential | 1 | 3 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM | 3 |
solute carrier family 2, facilitated glucose transporter member 3 | P11169 | Facilitative glucose transporter; present in platelet PM and α-granules; required for glucose uptake by platelets | 10 | 2 | Mascot, Sequest | FFE-IM, FFE-PM | 11 |
STIM1 | Q13586 | A Ca2+ sensor that links Ca2+ store depletion from the ER with store-operation Ca2+ influx from the PM | 1 | 5 | Sequest | FFE-IM, FFE-PM | 2 |
stomatin, isoform a | P27105 | Act as a cytoskeletal anchor in erythrocytes; present in platelet α-granules | 1 | 5 | Mascot, Sequest | biotin/NA, FFE-IM, FFE-PM, WGA | 12 |