Two novel thermally resistant endolysins encoded by pseudo T-even bacteriophages RB43 and RB49.

Identification and cloning of genes as well as biochemical characterization of the gene products were carried out for two novel endolysins of pseudo T-even lytic bacteriophages RB43 and RB49, which represent different myovirus groups of the subfamily Tevenvirinae. Genes RB43ORF159c and RB49р102 were cloned in E. coli cells, and their products were purified to electrophoretic homogeneity with an up to 80 % yield of total activity. In respect to substrate specificity, both enzymes were found to be lytic l-alanoyl-d-glutamate peptidases belonging to the M15 family. The pH optimum functioning of both endolysins was within the range 7.0-9.0, whereas the optimal values of ionic strength were different for the two proteins (25 mM vs 100 mM for the RB43 and RB49 endolysins respectively). Both peptidases were thermally resistant, with the RB43 endolysin being more stable (it restored 81 % of enzyme activity and 96 % of secondary structure after a 10 min heating at 90 °C) than its RB49 counterpart (27 and 77% respectively). The possible origin of genes of lytic l-alanoyl-d-glutamate peptidases of myoviruses as a result of horizontal transfer in the variable parts of genomes between unrelated phages having a common host is discussed.

Identification and characterization of the metal ion-dependent L-alanoyl-D-glutamate peptidase encoded by bacteriophage T5.

Although bacteriophage T5 is known to have lytic proteins for cell wall hydrolysis and phage progeny escape, their activities are still unknown. This is the first report on the cloning, expression and biochemical characterization of a bacteriophage T5 lytic hydrolase. The endolysin-encoding lys gene of virulent coliphage T5 was cloned in Escherichia coli cells, and an electrophoretically homogeneous product of this gene was obtained with a high yield (78% of total activity). The protein purified was shown to be an L-alanoyl-D-glutamate peptidase. The enzyme demonstrated maximal activity in diluted buffers (25-50 mM) at pH 8.5. The enzyme was strongly inhibited by EDTA and BAPTA, and fully reactivated by calcium/manganese chlorides. It was found that, along with E. coli peptidoglycan, peptidase of bacteriophage T5 can lyse peptidoglycans of other Gram-negative microorganisms (Pectobacterium carotovorum, Pseudomonas putida, Proteus vulgaris, and Proteus mirabilis). This endolysin is the first example of an L-alanoyl-D-glutamate peptidase in a virulent phage infecting Gram-negative bacteria. There are, however, a great many sequences in databases that are highly similar to that of bacteriophage T5 hydrolase, indicating a wide distribution of endolytic L-alanoyl-D-glutamate peptidases. The article discusses how an enzyme with such substrate specificity could be fixed in the process of evolution.