Calcium is essential for the major pseudopilin in the type 2 secretion system.

J Biol Chem

Department of Biochemistry, Biomolecular Structure Center, University of Washington, Seattle, Washington 98195, USA.

Published: September 2009

AI Article Synopsis

  • The pseudopilus is an essential component of the type 2 secretion system (T2SS), consisting of major pseudopilins that lack disulfide bridges unlike type 4 pilins.
  • Crystal structures of the major pseudopilin GspG in various bacteria reveal a crucial calcium ion at a specific site, indicating that calcium binding is vital for T2SS function.
  • Functional studies on GspG with mutations affecting calcium coordination demonstrate that calcium ions are necessary for the effective secretion of proteases by T2SS, contrasting with type 4 pilins which do not share this dependence.

Article Abstract

The pseudopilus is a key feature of the type 2 secretion system (T2SS) and is made up of multiple pseudopilins that are similar in fold to the type 4 pilins. However, pilins have disulfide bridges, whereas the major pseudopilins of T2SS do not. A key question is therefore how the pseudopilins, and in particular, the most abundant major pseudopilin, GspG, obtain sufficient stability to perform their function. Crystal structures of Vibrio cholerae, Vibrio vulnificus, and enterohemorrhagic Escherichia coli (EHEC) GspG were elucidated, and all show a calcium ion bound at the same site. Conservation of the calcium ligands fully supports the suggestion that calcium ion binding by the major pseudopilin is essential for the T2SS. Functional studies of GspG with mutated calcium ion-coordinating ligands were performed to investigate this hypothesis and show that in vivo protease secretion by the T2SS is severely impaired. Taking all evidence together, this allows the conclusion that, in complete contrast to the situation in the type 4 pili system homologs, in the T2SS, the major protein component of the central pseudopilus is dependent on calcium ions for activity.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2757947PMC
http://dx.doi.org/10.1074/jbc.C109.037655DOI Listing

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