The lytic enzyme in bacteriophage ψM1-induced lysates ofMethanobacterium thermoautotrophicumMarburg

The lytic enzyme from bacteriophage ψM1-induced lysates of Methanobacterium thermoautotrophicum was purified approx. 80-fold to near electrophoretic homogeneity. It was a 31-kDa monomeric, oxygen-sensitive pseudomurein endopeptidase hydrolysing the ?-Ala-Lys bond of pseudomurein. Pseudomurein endopeptidase-specific polyclonal antibodies reacted with a 31-kDa protein in crude extracts of non-infected host cells. This cross-reacting protein was purified. It did not exhibit lytic activity but its N-terminus was identical with the N-terminus of pseudomurein endopeptidase. The 31-kDa protein thus probably represents a pseudomurein endopeptidase whose autolytic activity is under control in non-infected, but deregulated in phage ψM1-infected cells. Its preferential location in the cell-wall area was demonstrated by immuno-electron microscopy and argued for a role of pseudomurein endopeptidase in the expansion of the cell wall during growth.