Table 2.
VirB/D4 subunit contacts, postulated functions and related components of effector translocator systems
| VirB proteins | Localization | Protein–protein contacts* | Proposed functions | Homologues‡ | |
|---|---|---|---|---|---|
| Dihybrid screen |
Biochemical assay |
||||
| Coupling protein | |||||
| VirD4 | IM | D4, E2 | D4, E2 | Recruitment of DNA and protein substrates to Mpf complex; translocase |
HP0524 (H.p.), DotL (L.p.), VirD4 (B.t.) |
| Channel subunits | |||||
| VirB6 | IM | B7, B9 | Assembly factor; channel subunit | PtlD (B.p.), VirB6 (Bart./Bruc.), TrwI1–5 (B.t.) | |
| VirB8 | IM | B1, B8, B9, B10 |
B8, B9, B10 | Assembly factor; bridge between subcomplexes; IM & OM VirB channel subunit |
HP0530 (H.p.), PtlE(B.p.), VirB8 (Bart./Bruc.), TrwG (B.t.) |
| VirB10 | IM | B8, B9, B10 | B8, B9, B10 | Bridge between IM & OM subcomplexes; channel subunit |
HP0527 (H.p.), PtlF (B.p.), DotB (L.p.), VirB10 (Bart./ Bruc.), TrwG (B.t.) |
| VirB3 | OM | PtlB (B.p.), VirB3 (Bart./Bruc.), TrwM (B.t.) | |||
| VirB7 | OM lipoprotein |
B7, B9 | B2, B6, B7, B9, 10 |
Stabilizes B9 by disulphide crosslink; B7–B9 dimer stabilizes other VirB proteins |
HP0532 (H.p.), PtlI(B.p.), VirB7 (Bart./Bruc.), TrwH1–5 (B.t.) |
| VirB9 | OM | B1, B7, B8, B9, B10, B11 |
B6, B7, B9, B10 |
OM pore? | HP0528 (H.p.), PtlF (B.p.), VirB9 (Bart./Bruc.), TrwF (B.t.) |
| Energetics | |||||
| VirB4 | IM | B4, B8, B10, B11 |
B4 | ATPase; homomultimer; energy for substrate export & pilus biogenesis |
CagE(H.p.), PtlC (B.p.), VirB4 (Bart./Bruc.), TrwF (B.t.) |
| VirB11 | IM | B4, B9 | B11 | ATPase; homomultimer; energy for substrate export & pilus biogenesis |
HP0525 (H.p.), PtlH (B.p.), DotB (L.p.) |
| Periplasmic factors | |||||
| VirB1 | Periplasm | B1, B4, B8, B9, B10, B1 |
Peptidoglycan hydrolase; channel assembly |
PtlE (B.p.), VirB1 (Bruc.), TrwN (B.t.) | |
| AcvB & VirJ | Periplasm | B1 to B11, D4, E2, D2 |
Possible periplasmic chaperones | ||
| T pilus | |||||
| VirB2 | IM, exocellular | B2, B5, B7 | Cyclized pilin subunit | PtlA (B.p.), VirB2 (Bart./ Bruc.), TrwL1-7 (B.t.) | |
| VirB5 | Periplasm, exocellular |
B2 | Pilus subunit, chaperone? | VirB5 (Bart./ Bruc.), TrwJ1-5 (B.t.) | |
| VirB7 | OM, exocellular |
B2 | Pilus assembly? | HP0532 (H.p.), Ptll(B.p.), VirB7 (Bart./Bruc.), TrwH1–5 (B.t.) |
|
| Effector translocator proteins associated with surface structures | |||||
| HP0532 (B7) (H.p.), HP0527 (B10) (H.p.) HP0529 (B9) (H.p.), DotO (L.p.), DotH (L.p.) |
|||||
Evidence for subunit–subunit contacts on the basis of results of yeast or bacterial dihybrid screens or biochemical assays. References are presented in the text.
Bacterial species are in parentheses: (Bart.) Bartonella henselae and B. tribocorum; (B.p.) B. pertussis; (Bruc.) Brucella spp.; (B.t.) Bartonella tribocorum; (H.p.) H. pylori; (L.p.) L. pneumophila. A comprehensive and continuously updated list of type IV secretion systems and gene–protein relationships can be found at Peter J. Christie’s laboratory website (see Online links). The Vir8 homologue HP0530 (H.p.) is reviewed in ref. 112. IM, inner membrane; OM, outer membrane; Mpf; mating pore formation.