Table 4.
Known T3S chaperones from selected animal- and plant-pathogenic bacteria
| Organisms and chaperonea | Interaction partner(s)b | Location of CBDc | Description/comments | Reference(s) |
|---|---|---|---|---|
| Yersinia spp. | ||||
| SycD (LcrH) (Ysc T3SS) | YopB (T), YopD (T), YscY (C), YscM1 (R), YscM2 (R) | aa 53 to 149 and 278 to 292 of YopD; no discrete CBD in YopB | Dimerizes; contains three TPRs; stabilizes YopB and YopD; regulatory function (see Fig. 7) | 69, 146, 147, 180, 181, 404, 489, 537 |
| SycE (Ysc T3SS) | YopE (E), YscM1 (R), YscM2 (R) | aa 15 to 50 of YopE | Dimerizes; promotes a disorder-to-order transition in the CBD of YopE; alanine substitutions in the CBD of YopE do not affect SycE binding and YopE secretion but lead to severely reduced translocation of YopE | 36, 37, 90, 169, 459, 460, 485, 489, 537, 604 |
| SycH (Ysc T3SS) | YopH (E), YscM1 (R), YscM2 (R) | aa 20 to 69 of YopH; N-terminal region of YscM2 | Dimerizes; YscM1 and YscM2 share aa similarity with the CBD of YopH; regulatory function (see Fig. 7) | 80, 168, 441, 604 |
| SycN, YscB (Ysc T3SS) | YopN (R/E) | aa 30 to 76 of YopN | SycN and YscB form a heterodimer and stabilize YopN | 126, 244, 494 |
| SycO (Ysc T3SS) | YopO (E), YscM1 (R) | aa 20 to 77 of YopO | Dimerizes; masks membrane localization domain of YopO; overproduction of SycO leads to reduced Yop secretion | 144, 314 |
| SycT (Ysc T3SS) | YopT (E) | At least aa 52 to 103 of YopT | Dimerizes; binding to catalytically inactive YopT(C139S) is reduced | 68, 240, 327 |
| YscE, YscG (Ysc T3SS) | YscF (N) | C-terminal region of YscF | YscE and YscG form a heterodimer; YscG contains TPRs and shares a similar fold with LcrH; YscE shares structural similarity with the needle protein MxiH from S. flexneri | 125, 440, 530 |
| YscY (Ysc T3SS) | YscX (EC) | aa 50 to 110 of YscX | Regulatory function (see Fig. 7) | 127, 241 |
| SycP (Ysa T3SS) | YspP (E) | Dimerizes; stabilizes YspP | 352 | |
| SycB (Ysa T3SS) | YspB (T), YspC (T) | Dimerizes; stabilizes YspB; together with the AraC-type regulator YscE regulates the expression of ysa T3S genes | 28, 178, 581 | |
| Shigella spp. | ||||
| IpgA | IcsB (E) | aa 171 to 247 of IcsB | Stabilizes IcsB; icsB and ipgA can be translated as a single fusion protein | 409 |
| IpgC | IpaB (T), IpaC (T), MxiE (R) | aa 15 to 45 and 48 to 74 of IpaB; aa 50 to 80 (213), 73 to 122 (422) and/or 33 to 73 (328) of IpaC | Dimerizes; contains TPR motifs; stabilizes IpaB and IpaC; probably acts as a coactivator of the AraC-type transcriptional activator MxiE (see Fig. 7) | 27, 35, 213, 328, 338, 354, 362, 422, 443 |
| IpgE | IpgD (E) | Stabilizes IpgD | 405 | |
| Spa15 | IpaA(E), IpgB1 (E), OspC3 (E), OspB (E), OspD1 (R) | aa 26 to 141 of OspC3; aa 263 to 365 of IpaA; aa 23 to 190 of IpgB1 | Dimerizes; is secreted; stabilizes IpgB but not IpaA; binds to the secreted antiactivator OspD1 and acts as coantiactivator (see Fig. 7) | 171, 422, 423, 565 |
| IpaD | IpaD (T) | Possesses self-chaperoning activity | 252 | |
| Salmonella spp. | ||||
| InvB (SPI-1) | SipA (SspA) (E), SopA (SipF) (E), SopE (E), SopE2 (E) | aa 1 to 45 of SopA; aa 1 to 158 of SipA; aa 30 to 45 of SopE | Dimerizes; contributes to stability of SopE2 and SipA; CBD of SopA is required for translocation; CBD of SopE prevents secretion by SPI-1 or flagellum in the absence of InvB | 58, 149–151, 219, 311, 321 |
| SicA (SPI-1) | SipB (T), SipC (T), InvF (R) | aa 80 to 100 of SipB | Self-interacts; coactivator of the AraC-type transcriptional regulator InvF; stabilizes SipB and SipC; SipB is stable and secreted in a sicA sipC mutant; CBD of SipB is not sufficient to target the protein to the translocation-associated T3SS | 119, 120, 271, 559 |
| SicP (SPI-1) | SptP (E) | aa 35 to 139 of SptP | Dimerizes; stabilizes SptP; translation of SicP is required for translation of SptP (translational coupling) | 76, 189, 520 |
| SigE (SPI-1) | SopB (SigD) (E) | Dimerizes; stabilizes SopB | 121, 231, 275, 340 | |
| SrcA (SPI-2) | SseL (E), PipB2 (E) | Dimerizes; multicargo T3S chaperone; the srcA gene is unlinked to the T3S system genomic region | 101 | |
| SscB (SPI-2) | SseF (E) | Stabilizes SseF | 115 | |
| SseA (SPI-2) | SseB (T), SseD (T) | aa 147 to 169 of SseB; aa 138 to 194 of SseD (but aa 32 to 82 of SseD also contribute to the binding of SseA) | Contributes to stability of SseB | 99, 472, 641, 642 |
| SsaE (SPI-2) | SseB (T) | Also contributes to secretion of the effector PipB | 369 | |
| SsaQS (SPI-2) | SsaQL (YscQ homolog) | Generated by tandem translation of ssaQL | 622 | |
| EPEC/EHEC | ||||
| CesA2 (L0017) | EspA (F) | Inhibits polymerization of EspA; stabilizes EspA | 527 | |
| CesAB (CesA) | EspA (F), EspB (T) | Dimerizes; stabilizes EspA | 111, 613 | |
| CesD | EspD (T) | Also contributes to secretion of EspB | 580 | |
| CesD2 | EspD (T) | Stabilizes EspD | 402 | |
| CesF | EspF (E) | 154, 575 | ||
| CesL | SepL (E) | 620 | ||
| CesT | Tir (E), Map (E), NleA (E), EspF (E), EspG (E), EspZ (E), NleG (E), NleH (E), NleH2 (E) | N-terminal 50 to 100 aa of Tir | Dimerizes; contributes to stability of Map; also contributes to secretion of effector NleI | 1, 109, 134, 153, 318, 340, 545, 546 |
| P. syringae | ||||
| HrpG | Unknown | Acts as suppressor of the negative regulator HrpV (see Fig. 7) | 593 | |
| ShcA | HopPsyA (HopA1) (E) | N-terminal 166 aa of HopPsyA | 564 | |
| ShcM | HopPtoM (HopM1) (E) | aa 100 to 400 of HopPtoM | Protects HopPtoM from Lon-mediated degradation | 22, 333 |
| ShcF | HopPtoF (HopF2) (E) | Stabilizes HopPtoF | 499 | |
| ShcV | HopPtoV (HopV1) (E) | aa 76 to 125 of HopPtoV | 592 | |
| ShcO1 | HopO1-1 (E), HopS1 (E), HopS2 (E) | Central part of HopO1-1 | Homologous to ShcS1; can interact with ShcS1 | 209, 259 |
| ShcS1 | HopO1-1 (E), HopS1 (E), HopS2 (E) | Central part of HopO1-1 | Can interact with ShcO1; forms homodimers | 209, 259 |
| ShcS2 | HopO1-1 (E), HopS1 (E), HopS2 (E) | Central part of HopO1-1 | Homologous to ShcS1 | 209 |
| X. campestris pv. vesicatoria | ||||
| HpaB | AvrBs1 (E), AvrBs3 (E), HpaA (E), HpaC (R) | aa 1 to 50 of AvrBs3; aa 225 to 275 of HpaA | Essential for pathogenicity; contributes to the efficient T3S and translocation of multiple effector proteins | 71, 73, 331 |
| Erwinia amylovora | ||||
| DspB/F | DspA/E (E) | aa 51 to 100 and C-terminal region of DspA/E | N-terminal CBD is required for DspA/E translocation (411); minimal translocation signal does not comprise CBD (556) | 193, 411, 556 |
a
T3S chaperones of translocation-associated T3S systems. For pathogens with more than one T3S system, the type of the respective T3S system is written in italics. Alternative protein names are given in parentheses. T3SS, T3S system.
b
Known interaction partners are categorized into effectors (E), translocon proteins (T), needle proteins (N), filament proteins (F), regulators (R), chaperones (C), and extracellular proteins of the T3S system (EC). Alternative protein names are given in parentheses.
c
aa, amino acids.