Function of the usher N-terminus in catalysing pilus assembly

Center for Infectious Diseases, Department of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, NY 11794-5120, USA.
Molecular Microbiology (Impact Factor: 4.42). 02/2011; 79(4):954-67. DOI: 10.1111/j.1365-2958.2010.07505.x
Source: PubMed


The chaperone/usher (CU) pathway is a conserved bacterial secretion system that assembles adhesive fibres termed pili or fimbriae. Pilus biogenesis by the CU pathway requires a periplasmic chaperone and an outer membrane (OM) assembly platform termed the usher. The usher catalyses formation of subunit-subunit interactions to promote polymerization of the pilus fibre and provides the channel for fibre secretion. The mechanism by which the usher catalyses pilus assembly is not known. Using the P and type 1 pilus systems of uropathogenic Escherichia coli, we show that a conserved N-terminal disulphide region of the PapC and FimD ushers, as well as residue F4 of FimD, are required for the catalytic activity of the ushers. PapC disulphide loop mutants were able to bind PapDG chaperone-subunit complexes, but did not assemble PapG into pilus fibres. FimD disulphide loop and F4 mutants were able to bind chaperone-subunit complexes and initiate assembly of pilus fibres, but were defective for extending the pilus fibres, as measured using in vivo co-purification and in vitro pilus polymerization assays. These results suggest that the catalytic activity of PapC is required to initiate pilus biogenesis, whereas the catalytic activity of FimD is required for extension of the pilus fibre.

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Available from: Tony W Ng
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    • "Ushers are located at the outer membrane of Gram-negative bacteria. These are ~ 90kDa proteins consisting of five distinct functional domains: a N-terminal periplasmic domain (UND) (Henderson et al., 2011; Eidam et al., 2008; Nishiyama et al., 2005; Nishiyama et al., 2003), a trans-membrane domain (TMD) (Remaut et al., 2008), a middle domain (UMD) (Huang et al., 2009; Yu et al., 2009; Remaut et al., 2008), and two C-terminal periplasmic domains (UCD1 and UCD2) (Phan et al., 2011; Dubnovitsky et al., 2010; Ford et al., 2010) (Fig. 1). "

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