Structure and dynamics of Pseudomonas aeruginosa ICP

QH301 Biology;QR Microbiology

Fu, Yinan ; Smith, Brian

University:University of Glasgow

Department:Institute of Molecular Cell and Systems Biology

关键词: chagasin, NMR, cathepsin, peptidase inhibitor, inhibitory activity, homology modelling;   

Others  :  http://theses.gla.ac.uk/723/1/2009fuphd.pdf

来源: University of Glasgow

【 摘 要 】

Pseudomonas aeruginosa inhibitor of cysteine peptidases (PA-ICP) is a potent protein inhibitor of papain-like cysteine peptidases (CPs) identified in Pseudomonas aeruginosa, an opportunistic pathogenic bacteria that can cause severe infections in human. It belongs to the newly characterized natural CP inhibitors of the I42 family, designated the ICP family. The members of this family are present in some protozoa and bacterial pathogens. They caninhibit both parasite and mammalian CPs with high affinity and specificity. Whether the main biological function of the proteins in the pathogens is to regulate the hydrolyticactivity of the organisms’ endogenous CPs or exogenous CPs so as to facilitate thepathogens’ invasion or survival is still under investigation. Although Pseudomonasaeruginosa contains a CP inhibitor, no CP genes are found in its genome, suggesting thatthe targets of PA-ICP may be exogenous. This hypothesis is supported by the presence of aputative secretion signal peptide at the N-terminus of PA-ICP which may be involved inexporting the protein to target exogenous CPs.In order to shed light on the biological function and inhibitory specificity of PA-ICP, thestructure and backbone dynamics of this protein were characterised using NMRspectroscopy. In this project, the inhibitory activity of PA-ICP to a range of mammalianmodel CPs was also studied. Like its previously studied homologs, PA-ICP adopts animmunoglobulin fold comprised of seven β-strands. Three highly conserved sequencemotifs located in mobile loop regions form the CP binding site. The inhibitor exhibits higheraffinity toward the mammalian CP cathepsin L than cathepsins H and B. Homologymodelling of the PA-ICP-cathspin L interaction based on the crystal structure of thechgasin-cathpsin L complex shows that PA-ICP may inhibit the peptidases by blockingthe enzyme’s active site and that the interactions between chagasin and CPs may beconserved in PA-ICP-peptidase complexes. The specificity of the inhibitors may bedetermined by the relative flexibility of the loops bearing the binding site motifs and theelectrostatic properties of certain residues near the binding sites.