Formation of functional Tat translocases from heterologous components

Matthew G Hicks,David Guymer,David A Widdick,Ben C Berks,Tracy Palmer,Isabelle Caldelari,Grant Buchanan

doi:10.1186/1471-2180-6-64

Matthew G Hicks, David Guymer + Show 5 more

Open Access

https://doi.org/10.1186/1471-2180-6-64

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Abstract

BackgroundThe Tat pathway transports folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of plants. In Eschericha coli, Tat transport requires the integral membrane proteins TatA, TatB and TatC. In this study we have tested the ability of tat genes from the eubacterial species Pseudomonas syringae, Streptomyces coelicolor and Aquifex aeolicus, to compensate for the absence of the cognate E. coli tat gene, and thus to form functional Tat translocases with E. coli Tat components.ResultsAll three subunits of the Tat system from the Gram positive organism Streptomyces coelicolor were able to form heterologous translocases with substantive Tat transport activity. However, only the TatA and TatB proteins of Pseudomonas syringae were able to functionally interact with the E. coli Tat system even though the two organisms are closely related. Of the Tat components from the phylogenetically distant hyperthermophillic bacterium Aquifex aeolicus only the TatA proteins showed any detectable level of heterologous functionality. The heterologously expressed TatA proteins of S. coelicolor and A. aeolicus were found exclusively in the membrane fraction.ConclusionOur results show that of the three Tat proteins, TatA is most likely to show cross-species complementation. By contrast, TatB and TatC do not always show cross-complementation, probably because they must recognise heterologous signal peptides. Since heterologously-expressed S. coelicolor TatA protein was functional and found only in the membrane fraction, it suggests that soluble forms of Streptomyces TatA reported by others do not play a role in protein export.

Highlights

The Tat pathway transports folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of plants
We have systematically examined the ability of tat genes from three different bacterial species to compensate for the absence of the cognate E. coli tat gene
None-the-less, these results suggest that TatA proteins from all of the three species tested are capable of some level of heterologous interaction with the E. coli TatBC proteins

Summary

Introduction

The Tat pathway transports folded proteins across the cytoplasmic membrane of bacteria and the thylakoid membrane of plants. In Eschericha coli, Tat transport requires the integral membrane proteins TatA, TatB and TatC. In this study we have tested the ability of tat genes from the eubacterial species Pseudomonas syringae, Streptomyces coelicolor and Aquifex aeolicus, to compensate for the absence of the cognate E. coli tat gene, and to form functional Tat translocases with E. coli Tat components. There are two general pathways by which proteins are translocated across the cytoplasmic membranes of bacteria. The Sec pathway, which is ubiquitous, uses a threading mechanism to transport unfolded polypeptides across the membrane, driven by the energy of ATP hydrolysis and the transmembrane proton gradient [1]. Percentage identity to E. coli homologue E. coli TatA P. syringae TatA.

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