Early Contacts between Substrate Proteins and TatA Translocase Component in Twin-arginine Translocation

Abstract

Background:The membrane proteins, TatA, TatB, and TatC, enable the transmembrane passage of folded precursor proteins. Results: The transmembrane helix of TatA makes contacts with TatC and precursors recognized by the TatBC complex. Conclusion: Following its insertion into the TatBC receptor complex, a Tat signal sequence contacts a nearby monomer of TatA. Significance: TatA interacts with twin-arginine precursors prior to the actual translocation event.

Direct Interaction between a Precursor Mature Domain and Transport Component Tha4 during Twin Arginine Transport of Chloroplasts

“…More recently, the bacterial precursor pSufI was shown to be "in the immediate proximity of" TatA when supersaturating conditions of precursor were present (Panahandeh et al, 2008), suggesting the formation of a translocation intermediate. It was also demonstrated that the mature domain of SufI could be cross linked to TatB and TatA (Maurer et al, 2010), and the signal peptides of the precursors of SufI or a chimeric protein, TorA-mCherry, could be linked to TatA (Fröbel et al, 2011). The latter study demonstrated that the interaction was likely not kinetically related to transport: the TatA Cys variants used are largely inactive and the interaction shows no time dependence, occurring faster than the assay could measure (Fröbel et al, 2011).…”

Mapping the Signal Peptide Binding and Oligomer Contact Sites of the Core Subunit of the Pea Twin Arginine Protein Translocase

“…It forms a homooligomer to which Hcf106 (TatB) binds to assemble the receptor complex (Behrendt et al, 2007;Orriss et al, 2007); it binds to the signal peptide Alami et al, 2003;Gérard and Cline, 2006); it probably serves as the organizing center for Tha4 assembly (Fröbel et al, 2011;Rollauer et al, 2012); and it may provide the motive force for transmembrane protein movement (Brüser and Sanders, 2003;Dabney-Smith et al, 2006;Cline and McCaffery, 2007). Yet the molecular determinants of these different functions are largely unknown.…”

Assembly pathway of a bacterial complex iron sulfur molybdoenzyme

“…Substrate protein recognition by the TatBC complex subsequently results in the recruitment and oligomerization of TatA protomers to form the active translocon pore using energy from the proton motive force (86,87). As the purported protein-conducting channel, the TatA multi-protomer pore unit must be large enough to permit passage of large protein substrates possessing secondary, tertiary, and in many cases quaternary structure with sizes ranging from ~10 kDa to ~140 kDa (88)(89)(90). Following translocation initiation from the TatBC recognition unit, substrates are translocated through the TatA multimer pore across the cytoplasmic membrane utilizing the electrochemical gradient (86,88,(90)(91)(92)(93).…”

“…Following translocation initiation from the TatBC recognition unit, substrates are translocated through the TatA multimer pore across the cytoplasmic membrane utilizing the electrochemical gradient (86,88,(90)(91)(92)(93). Several studies have found that the substrate protein interacts with TatA and TatBC separately, suggesting that the translocon is not fully assembled until receiving a substrate (88)(89)(90)94). Currently, it is proposed that both TatA and TatB use the same binding site on TatC, and since TatB occupies this site in the resting TatBC complex, TatA must displace TatB form the site at some stage in the translocation cycle (95).…”

“…As the purported protein-conducting channel, the TatA multi-protomer pore unit must be large enough to permit passage of large protein substrates possessing secondary, tertiary, and in many cases quaternary structure with sizes ranging from ~10 kDa to ~140 kDa (88)(89)(90). Following translocation initiation from the TatBC recognition unit, substrates are translocated through the TatA multimer pore across the cytoplasmic membrane utilizing the electrochemical gradient (86,88,(90)(91)(92)(93). Several studies have found that the substrate protein interacts with TatA and TatBC separately, suggesting that the translocon is not fully assembled until receiving a substrate (88)(89)(90)94).…”