TCDB is operated by the Saier Lab Bioinformatics Group
TCIDNameDomainKingdom/PhylumProtein(s)
*3.A.23.1.1









Type VI secretion system (T6SS) VasA-L + Vca0107-09; + Vca0123 + Vc1416 (Pukatzki et al., 2006; Pukatzki et al., 2007). This secretion system displays antimicrobial properties (Macintyre et al., 2010).  It functions like contractile tails of phage and penetrates cells with a trimeric VgrG spike protein to which are associated PAAR repeat proteins that sharpen the tip of the spike and are released into the cytoplasm of the target cell (Shneider et al. 2013). Certain Vibrionaceae adapted their antibacterial T6SS to mediate interactions with eukaryotic hosts or predators, promoting their toxicity (Dar et al. 2018).

Bacteria
Proteobacteria
Vca0107-0109 + VasA-L + Vca0123 + Vc1416 of Vibrio cholerae
Vca0107 (168 aas) (NP_232508)
Vca0108 (492 aas) (NP_232509)
Vca0109 (145 aas) (NP_232510)
VasA (Vca0110; 589 aas; 0-2 C-terminal TMSs) (AAF96024)
VasB (Vca0111; 338 aas; 0 TMSs) (AAF96025)
VasC (Vca0112; 495 aas; 0 TMSs) (AAF96026)
VasD (Vca0113; 158 aas; 1 N-terminal TMS) (AAF96027)
VasE (Vca0114; 444 aas; 0[-19?] TMSs) (AAF96028)
VasF (resembles IcmH) (Vca0115; 257 aas; 1[-4?] TMSs) (AAF96029)
VasG (ClpB) (Vca0116; 869 aas; 0[-3?] TMSs) (AAF96030)
VasH (sigma-54 dep. Tx activator) (Vca0117; 530 aas; 0 TMSs) (AAF96031)
VasI (Vca0118; 227 aas; 1 N-terminal TMS) (AAF96032)
VasJ (Vca0119; 469 aas; 0[-4] TMSs) (AAF96033)
VasK (resembles IcmF) (Vca0120; 1181 aas; 2 N-terminal TMSs) (AAF96034)
VasL (Vca0121; 421 aas; 1 central TMS) (AAF96035) Vc1416/KgrG (1163 aas) (NP_231059)
Vca0123 (/VgrG 1017 aas) (NP_232524)
Possible cell puncture device, VgrG-1, G-2, G-3 of Vibrio cholera Type VII S-5.
VgrG-1 (197 aas) (A1F9V7)
VgrG-2 (694 aas) (A3E8Q2) (like EupI of E. tarda)
VgrG-3 (1017 aas) (B2D7K2)
*3.A.23.2.1









Type VI secretion system, EvpA-P (Zheng and Leung, 2007)
Bacteria
Proteobacteria
EvpA-P of Edwardsiella tarda
EvpA, 171 aas (Q6EE21)
EvpB, 495 aas (Q6EE20)
EvpC, 163 aas (Q6EE19)
EvpD, 407 aas (Q6EE18)
EvpE, 158 aas (Q6EE17)
EvpF, 613 aas (Q6EE16)
EvpG, 341 aas (Q6EE15)
EvpH, 870 aas (Q6EE14)
EvpI, 661 aas (A8YQR5)
EvpJ, 100 aas (A8YQR6)
EvpK, 335 aas (A8YQR7)
EvpL, 235 aas (A8YQR8)
EvpM, 462 aas (A8YQR9)
EvpN, 216 aas (A8YQS0)
EvpO, 1263 aas (A8YQS1)
EvpP, 185 aas (A8YQR4)
*3.A.23.3.1









Type VI secretion system TssA - TssG plus TssI - TssM (Cianfanelli et al. 2016).

Bacteria
Proteobacteria
Type VI secretion system TssA - TssG plus TssI - TssM of Campylobbacter jejuni
TssA, 415 aas
TssB, 161 aas
TssC, 484 aas
TssD, 171 aas
TssE, 130 aas
TssF, 573 aas
TssG, 302 aas
TssI, 838 aas
TssJ, 148 aas
TssK, 465 aas
TssL, 257 aas
TssM, 1175 aa
*3.A.23.4.1









Type VI secretion system, TssA - TssH plus TssK - TssM (Cianfanelli et al. 2016).

Bacteria
Proteobacteria
Type VI secretion system, TssA - TssH plus TssK - TssM of Acinetobacter baumannii
TssA, 364 aas
TssB, 167 aas
TssC, 493 aas
TssD (Hcp), 167 aas
TssE (lysozyme), 158 aas
TssF (ImpG; VasA), 603 aas
TssG, 332 aas
TssH, 894 aas
TssK, 454 aas
TssL, 268 aas
TssM, 1252 aa
*3.A.23.5.1









Type VI secretion system, TssB - TssM (Cianfanelli et al. 2016).

Bacteria
Proteobacteria
TssB - TssM of Geobacullus sulfurreducens
TssB, 161 aas
TssC, 494 aas
TssD, 161 aas
TssE, 135 aas, needle hub
TssF, 577 aas
TssG, 330 aas
TssH, 875 aas
TssI, 697 aas, needle syringe
TssJ, 814 aas
TssK, 463 aas
TssL, 227 aas
TssM, 1154 aa
*3.A.23.6.1









To interact with other cells, bacteria use contractile machines that function similarly to membrane-puncturing bacteriophages. The so-called type 6 secretion system (T6SS) functions from inside a bacterial cell. Böck et al. used modern electron microscopy methods and functional assays to resolve the structure and function of a T6SS in the cellular context. They identified three modules and showed large-scale structural changes upon firing. T6SSs are organized in multibarrel gun-like arrays and may contribute to the survival of bacteria inside their host. 

Contractile injection systems (CISs) deliver effectors to mediate bacterial cell-cell interactions. Their structural components are homologous to the contractile tails of phages (1). CISs consist of an inner tube surrounded by a contractile sheath, a spike capping the inner tube, and a baseplate complex at the base of the sheath. Sheath contraction propels the inner tube into the target. Two modes of action divide CISs into “extracellular CISs” (eCISs) and “type 6 secretion” (T6S) systems (T6SSs). eCISs resemble headless phages; they are released into the medium and bind to the target cell surface. Examples are antibacterial R-type bacteriocins (Leiman and Shneider 2012), insecticidal antifeeding prophages (Afps) (Hurst et al. 2004), and metamorphosis-inducing structures (MACs) (Shikuma et al. 2014). By contrast, the T6SS is defined by its cytoplasmic localization and anchoring to the inner membrane (Basler et al. 2012; Hachani et al. 2016); Chang et al. 2017).

Amoebophilus asiaticus is an obligate intracellular bacterial symbiont of amoebae. The Amoebophilus genome does not encode known secretion systems, but it contains a gene cluster with similarities to that of Afps. Böck et al. 2017 reasoned that the Afp-like gene cluster might encode a system that would give insight into T6SS structure, function, and evolution.

Thus, the Amoebophilus Afp-like gene cluster encodes a T6SS (Böck et al. 2017). Sequence analyses indicated a close relationship to eCISs, and the term “T6SS subtype 4” (T6SSiv) was therefore introduced. In contrast to the distant relationships of T6SSi-iii to eCISs and phages that obstruct the reconstruction of an evolutionary path (1, 24), it can be hypothesized that T6SSiv evolved from an Afp/MAC-like eCIS (independently of T6SSi-iii) by the loss of tail fibers, loss of holin, and the establishment of interactions with the cytoplasmic membrane. Alternatively, T6SSiv represents a primordial system from which eCISs, phages, and T6SSi-iii evolved. T6SSiv-like gene clusters were detected in six diverse bacterial phyla. The finding that diverse T6SS subtypes do not share a conserved gene set that would distinguish them from eCISs or phages emphasizes the necessity of an integrative approach to discover and characterize new systems. This situation is reminiscent of type IV secretion systems (3.A.7).

Bacteria
Bacteroidetes
T6SS of Amoebophilus asiaticus:  The proteins listed are those in the T6SS gene cluster although several of them may not be involved in Type 6 secretion.
B3ET73 of 599 aas and 0 TMSs. Like Spike protein (T4 gp5) (Homologous to constituents (i.e., A8YQR5 in 3.A.23.2.1) and other T6SS systems).
B3ET74 of 102 aas and 0 TMSs. Like Tip protein (T4 gp5.4) (Homologous to constituents (i.e., A8YQR6 in 3.A.23.2.1) of T6SSs).
B3ET75 of 131 aas and 0 TMSs. Like Baseplate (T4 gp25). Resembles TC# 1.K.1.1.1; tail lysozyme).
B3ET76 of 831 aas and 0 TMSs. Like Baseplate (T4 gp25). (A part resembles a part of C3L421 in this same system (3.A.23.6.1)).
C3L421 of 1,561 aas and 0 TMSs.  Like Tape measure protein (T4 gp29). (A part resembles a part of B3ET76 in this same system (3.A.23.6.1)).
B3ERV5 of 247 aas and 0 TMSs.  Like Baseplate (T4 gp48)
B3ERV6 of 1258 aas and 0 - 2 TMSs. Like Baseplate (T4 gp6)
B3ERW2 of 1121 aas and 19 TMSs in a 6 = 1 = 1 = 1 =4 + 6 arrangement. Like Baseplate T4 gp27). TC Blast reveals that the first 13 TMSs hit many members of the SSS family (TC# 2.A.1).
B3ERW3 of 314 aas and 0 or 1 TMSs. Of unknown function in T4
B3ET61 of 169 aas and 1 N-terminal TMS.  Like Baseplate (T4 gp53)
B3ET62 of 331 aas and 0 TMSs.  Like glyceraldehyde 3P dehydrogenase.
B3ERD7 of 274 aas and 1 C-terminal TMS. Possibly an IS4-type transposase.
B3ET64 of 347 aas and 1 N-terminal TMS. Like ankyrin.  Has many short (12 - 18 aa) repeats and hits many proteins in TCDB including TC families 1.A.4, 8.A.28 (ankyrin), 9.A.3 (containing ankyrin repeats), 1.I .1, etc.
B3ET65 of 193 aas and 0 TMSs.  Like Tail terminator protein (T4gp15)
B3ET66 of 282 aas and 0 TMSs.  Like an Afp-like protein of unknown function in T4
B3ET67 of 498 aas and 0 TMSs.  Like a tail sheath protein (T4 gp18). Hits TC# 1.K.1.1.1.
B3ET68 of 167 aas and 0 TMSs.  Like an Afp-like protein of unknown function
B3ET69 of 148 aas and 0 TMSs.  Like an Afp-like protein of unknown function
B3ET70 of 154 aas and 0 TMSs.  Like a tube protein (T4gp19)
B3ET71 of 59 aas and 0 TMSs.  Like an Afp protein of unknown function.
B3ET72 of 377 aas and 0 TMSs. Like a baseplate protein (T4 gp54)