The lytic enzyme of the pneumococcal phage Dp‐1: a chimeric lysin of intergeneric origin

Abstract

SummaryWe have localized, cloned and characterized the genes coding for the lytic system of the pneumococcal phage Dp-1. The lytic enzyme of this phage (Pal), previously identified as an N-acetyl-muramoyl-L-alanine amidase, shows a modular organization similar to that described for the lytic enzymes of Streptococcus pneumoniae and its bacteriophages. The construction of chimeric enzymes between pneumococcus and bacteria (or phages) that belong to different Gram-positive families has shown that the interchange of functional domains switches enzyme specificity. Interestingly, Pal appears to be a natural chimeric enzyme of intergeneric origin, that is the N-terminal domain was highly similar to that of the murein hydrolase coded by a gene found in the phage BK5-T that infects Lactococcus lactis, whereas the C-terminal domain was homologous to those found in the lytic enzymes of the pneumococcal system that is responsible for the binding to the choline residues present in the cell wall substrate. Biochemical analysis of Pal revealed that this enzyme shares important properties with those of the major LytA101 autolysin found in an atypical, clinical pneumococcal isolate. These peculiar characteristics have been ascribed to a modified C-terminal domain. The natural chimeric enzyme described here provides further support for the theory of modular evolution of proteins and its characteristics also furnish interesting clues on the molecular mechanisms involved in the more invasive types of atypical pneumococci.

Autolysins of Bacillus subtilis: multiple enzymes with multiple functions

“…yqeE, which is near to but outside skin, could be another such gene. The existence of such genes implies exchange of peptidoglycan hydrolase genes between the host and its phages, a phenomenon that has also been described in pneumococci (Sheenan et al, 1997). xlyB, a putative amidase gene of the XlyB family, lies near to but outside PBSX.…”

Sequence analysis of the lactococcal bacteriophage bIL170: insights into structural proteins and HNH endonucleases in dairy phages The GenBank/EMBL/DDBJ accession numbers for the sequences reported in this paper are bIL170, AF009630; bIL120, AY054975; bIL15, AY054976; bIL191, AY054977; bIL77, AY054978.

“…The bIL170 endolysin looks as if it is a chimera between the catalytic N-terminal domain shared by phages of the 936 group and a C-terminal domain found in other lactococcal phages. Such natural chimeras have been found in different bacteriophages (Fastrez, 1996 ;Sheehan et al, 1997) and are likely to play a role in evolution of host range.…”

Bioinformatics analysis of bacteriophage and prophage endolysin domains

“…From the evolutionary point of view, it has been postulated that these enzymes may have evolved by the interchange of phage and bacterial genes encoding the individual modules. An evolutionary relationship between phage endolysins and bacterial lytic enzymes (autolysins) was originally proposed by Garcia et al (1988) and it gained a strong support by the creation of functional chimeric phage-bacterial enzymes -one domain was of phage origin, whereas the other domain was of bacterial origin (Diaz et al 1991), or by the existence of natural chimeric endolysins of intergeneric origin (Sheehan et al 1997). Such an assumed evolutionary relationship between endolysins and autolysins would be another example of horizontal gene transfer between bacteriophages and their host bacterial cells, an event also reported for other genes (Hambly & Suttle 2005).…”