Journal Article Crystal structure of the flexible tandem repeat domain of bacterial cellulose synthesis subunit C

Nojima, Shingo  ,  Fujishima, Ayumi  ,  Kato, Koji  ,  Ohuchi, Kayoko  ,  Shimizu, Nobutaka  ,  Yonezawa, Kento  ,  Tajima, Kenji  ,  Yao, Min

7p.13018 , 2017-10-12 , Nature Publishing Group
Bacterial cellulose (BC) is synthesized and exported through the cell membrane via a large protein complex (terminal complex) that consists of three or four subunits. BcsC is a little-studied subunit considered to export BC to the extracellular matrix. It is predicted to have two domains: a tetratrico peptide repeat (TPR) domain and a beta-barrelled outer membrane domain. Here we report the crystal structure of the N-terminal part of BcsC-TPR domain (Asp24-Arg272) derived from Enterobacter CJF-002. Unlike most TPR-containing proteins which have continuous TPR motifs, this structure has an extra a-helix between two clusters of TPR motifs. Five independent molecules in the crystal had three different conformations that varied at the hinge of the inserted a-helix. Such structural feature indicates that the inserted a-helix confers flexibility to the chain and changes the direction of the TPR super-helix, which was also suggested by structural analysis of BcsC-TPR (Asp24-Leu664) in solution by size exclusion chromatography-small-angle X-ray scattering. The flexibility at the a-helical hinge may play important role for exporting glucan chains.

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