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TatABCE translocase. Early contacts between substrate proteins and TatA have been demonstrated (Fröbel et al., 2011). TatC helix 5 and the TatB transmembrane helix interact (Kneuper et al., 2012).  TatC functions as an obligate oligomer (Cleon et al. 2015). TatA is the most abundant component of the complex and facilitates assembly of this complex.It exhibits a uniform distribution throughout the inner membrane, but forms linear clusters upon increased expression of TatBC (Smith et al. 2017).  TatA and TatB both have the capacity to bind at two TatC sites, one in TMS5 and one in TMS6 (Habersetzer et al. 2017). However in vivo this is regulated according to the activation state of the complex. In the resting-state system, TatB binds the polar cluster site in TMS 5 with TatA occupying the site in TMS 6. However, when the system is activated by overproduction of a substrate, TatA and TatB switch binding sites. Habersetzer et al. 2017 proposed that this substrate-triggered positional exchange is a key step in the assembly of an active Tat translocase. A  highly conserved glutamate residue in the transmembrane region of E. coli TatC, which, when modified by DCCD, interferes with the deep insertion of a Tat signal peptide into the TatBC receptor complex (Blümmel et al. 2017). Different from TatA but rather like TatB, TatE contacts a Tat signal peptide independently of the proton-motive force and restricts the premature processing of a Tat signal peptide (Eimer et al. 2018). Furthermore, TatE embarks at the transmembrane helix five of TatC where it becomes so closely spaced to TatB that both proteins can be covalently linked by a zero-space cross-linker. This suggests that in addition to TatB and TatC, TatE is a component of the Tat substrate receptor complex. A bioinformatic analysis revealed a relatively broad distribution of tatE genes in bacterial phyla and highlights unique protein sequence features of TatE orthologs (Eimer et al. 2018). A TatA/TatB binding site on the TatC component of the E. coli Tat tanslocase has been identified (Severi et al. 2023).

TatABCE of E. coli

Twin arginine targeting protein translocase, TatABC (Kimura et al. 2006).

TatABC (MXAN_2960, MXAN5905-4) of Myxococcus xanthus.

TatABCE.  The twin-arginine translocation (Tat) system transports large folded proteins containing a characteristic twin-arginine motif in their signal peptide across membranes. Together with TatB, TatC is part of a receptor directly interacting with Tat signal peptides (Eimer et al. 2015; Kuzniatsova et al. 2016; Cléon et al. 2015).

TatABCE of Bdellovibrio bacteriovorus

Mitochondrial twin arginine (TatA/TatC) protein translocase.  This system has been shown to be active in E. coli (Petrů et al. 2018). Many mitochondria have lost the Tat system, while some retain only the TatC subunit.  Only those that have both TatC and TatA seem to be active (Petrů et al. 2018).

TatC/TatA of Andalucia godoyi (Jakobid flagellate)
TatC, 253 aas; M4QCS0
TatA, 52 aas; M4Q9A7

The chloroplast Tat translocase (cpTatC/Hcf106/Tha4) (Gérard and Cline, 2007).  The precursor mature domain of the substrate protein interacts directly with Tha4 (Pal et al. 2012).  Hcf106 is predicted to contain a single amino terminal transmembrane domain followed by a Pro-Gly hinge, a predicted amphipathic alpha-helix (APH), and a loosely structured carboxy terminus.  The amphipathic α-helix interacts with the bilayer (Zhang et al., 2013a; Zhang et al. 2013b).  TatA has structural plasticity and a capability to adapt to local environments (Pettersson et al. 2018).

Viridiplantae, Streptophyta
cpTatC/Hcf106/Tha4 of Arabidopsis thaliana
cpTatC (TatC or MttB family; APG2; albino and pale green 2; 340 aas) (Q9SJV5)
Hcf106 (TatA or MttA family; 260 aas) (Q9XH75)
Tha4 (TatA or MttA family; 147 aas) (Q9LKU2)

Sec-independent protein translocase, TatABC (Widdick et al. 2006).

Sec-independent protein translocase protein TatACB of Streptomyces coelicolor

TatA (Q9RJ68)
TatB (Q9FBK8)
TatC (Q9RJ69)

TatAd/Cd translocase (Jongbloed et al., 2004).  The intrinsic ability of TatA to flip out of the membrane core may play a role in its membrane-destabilizing effect during Tat-dependent translocation (Stockwald et al. 2022).

TatAd/Cd of Bacillus subtilis
TatAd (70 aas; O31467)
TatCd (245 aas; P42252)

TatAy/Cy translocase (Jongbloed et al., 2004)
TatAy/Cy of Bacillus subtilis
TatAy (57 aas; O05522)
TatCy (254 aas; O05523)

Twin arginine (TatA0 (90 aas, 1 TMS)/TatC (441 aas, 6 TMSs with a hydrophilic N-terminal domain) protein translocase (Dilks et al. 2005; Giménez et al. 2007; Szabo and Pohlschroder 2012; Ghosh et al. 2019).

Twin arginine translocase, TatAC0 of Haloferax volcanii
TatA0 (D4GVK4)
TatC0 (D4GZD0) 

Twin Arginine (TatAt (91 aas and 1 TMS)/TatCt (718 aas and 14 TMSs) protein translocase (Dilks et al. 2005; Giménez et al. 2007; Szabo and Pohlschroder 2012; Ghosh et al. 2019).  The Tat system exports almost the entire secretome in many haloarchaea including this one (Ghosh et al. 2019).

Tat system, TatACt of Haloferax volcanii
TatAt (91aas) (D4GWC8)
TatCt (718aas; duplicated with 6 + 2 +6 = 14 putative TMSs) (D4GWC9) 

A Tat system, TatC of 365 aas and 6 TMSs, and a potential TatB of 71 aas and 1 TMS.

Candidatus Saccharibacteria
Tat (TatBC) system of Candidatus Saccharibacteria bacterium  

Tat (TatCB) system consisting of TatC (238 aas and 5 or 6 TMSs) and TatB (73 aas and 1 TMS).

Candidatus Saccharibacteria
TatBC of Candidatus Saccharibacteria bacterium

Tat system consisting of TatC (355 aas and 5 or 6 TMSs) and putative TatB (62 aas and 1 TMS). The tat genes are flanked by a sortase gene (WP_104944876) and a groL chaparone protein-encoding gene (WP_104944880).

Candidatus Saccharibacteria
TatBC of Candidatus Saccharibacteria bacterium