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Volume 2015, Article ID 828693, 12 pages
http://dx.doi.org/10.1155/2015/828693
Research Article

Biochemical Characterisation of Phage Pseudomurein Endoisopeptidases PeiW and PeiP Using Synthetic Peptides

AgResearch Limited, Grasslands Research Centre, Tennent Drive, Private Bag 11008, Palmerston North 4442, New Zealand

Received 27 May 2015; Accepted 13 August 2015

Academic Editor: Sonja-Verena Albers

Copyright © 2015 Linley R. Schofield et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Pseudomurein endoisopeptidases cause lysis of the cell walls of methanogens by cleaving the isopeptide bond Ala-ε-Lys in the peptide chain of pseudomurein. PeiW and PeiP are two thermostable pseudomurein endoisopeptidases encoded by phage ΨM100 of Methanothermobacter wolfei and phages ΨM1 and ΨM2 of Methanothermobacter marburgensis, respectively. A continuous assay using synthetic peptide substrates was developed and used in the biochemical characterisation of recombinant PeiW and PeiP. The advantages of these synthetic peptide substrates over natural substrates are sensitivity, high purity, and characterisation and the fact that they are more easily obtained than natural substrates. In the presence of a reducing agent, purified PeiW and PeiP each showed similar activity under aerobic and anaerobic conditions. Both enzymes required a divalent metal for activity and showed greater thermostability in the presence of Ca2+. PeiW and PeiP involve a cysteine residue in catalysis and have a monomeric native conformation. The kinetic parameters, and , were determined, and the ε-isopeptide bond between alanine and lysine was confirmed as the bond lysed by these enzymes in pseudomurein. The new assay may have wider applications for the general study of peptidases and the identification of specific methanogens susceptible to lysis by specific pseudomurein endoisopeptidases.