Ultrastructural characterisation of Bacillus subtilis TatA complexes suggests they are too small to form homooligomeric translocation pores

作者：Beck Daniel; Vasisht Nishi; Baglieri Jacopo; Monteferrante Carmine G; van Dijl Jan Maarten; Robinson Colin; Smith Corinne J^*

来源：Biochimica et Biophysica Acta-Molecular Cell Research, 2013, 1833(8): 1811-1819.

DOI：10.1016/j.bbamcr.2013.03.028

• Tat translocation
• Protein transport
• Gram positive bacteria
• Electron microscopy
• Single particle image processing

Tat-dependent protein transport permits the traffic of fully folded proteins across membranes in bacteria and chloroplasts. The mechanism by which this occurs is not understood. Current theories propose that a key step requires the coalescence of a substrate-binding TatC-containing complex with a TatA complex, which forms pores of varying sizes that could accommodate different substrates. We have studied the structure of the TatAd complex from Bacillus subtilis using electron microscopy to generate the first 3D model of a TatA complex from a Gram-positive bacterium. We observe that TatAd does not exhibit the remarkable heterogeneity of Escherichia colt TatA complexes but instead forms ring-shaped complexes of 7.5-9 nm diameter with potential pores of 2.5-3 nm diameter that are occluded at one end. Such structures are consistent with those seen for E. coli TatE complexes. Furthermore, the small diameter of the TatAd pore, and the homogeneous nature of the complexes, suggest that TatAd cannot form the translocation channel by itself. Biochemical data indicate that another B. subtilis TatA complex, TatAc, has similar properties, suggesting a common theme for TatA-type complexes from Bacillus.

• 出版日期2013-8