The autolytic ('suicidase') system of Enterococcus hirae: From lysine depletion autolysis to biochemical and molecular studies of the two muramidases of Enterococcus hirae ATCC 9790

Abstract

Autolysis of Enterococcus hirae ATCC 9790 is the result of the action of endogenous enzymes that hydrolyze bonds in the protective and shape-maintaining cell wall peptidoglycan. It is thought that these potentially suicidal enzymes play a positive role(s) in wall growth and division and are expressed as autolysins when cell wall assembly and/or repair are inhibited. E. hirae possesses two potentially autolytic enzymes, both of which are muramidases. Although they hydrolyze the same bond as hen egg-white lysozyme, both are high-molecular-mass, complex enzymes. Muramidase-1 is synthesized as a zymogen, requiring protease activation. It is a glucoenzyme that is also multiply nucleotidylated with an unusual nucleotide, 5-mercaptouridine monophosphate. Muramidase-2 is almost certainly a product of a separate gene. The deduced amino acid sequence of a cloned gene for extracellular muramidase-2 showed several unusual features. It appears to be a two-, or perhaps three-domain protein with a putative glycosidase-active site near the N-terminal end and six 45-amino-acid-long repeats at the C-terminal end which are presumed to be involved with high-affinity binding to the insoluble peptidoglycan substrate. Muramidase-2 binds penicillin with low affinity. The presence of several amino acid groupings characteristic of serine-active site beta-lactam-interactive proteins is consistent with the possible presence of a penicillin-binding, third domain. Indirect evidence consistent with a role(s) for these enzymes in cell wall growth and division has been obtained. However, proof of such role(s) awaits modern genetic, molecular, and biochemical analyses.

A Novel Putative Enterococcal Pathogenicity Island Linked to theespVirulence Gene ofEnterococcus faeciumand Associated with Epidemicity

“…The muramidase gene is predicted to encode an enzyme with important physiological functions during cell growth and division (52,53,56). Most of these enzymes have a domain structure (42).…”

Les autolysines des bactéries lactiques

“…Notons que certaines autolysines ont été identifiées dans le milieu extracellulaire comme une muramidase de C acetobutylicum (Croux et al, 1992) ou encore l'amidase et la glucosaminidase de S aureus codée par le gène unique atl (Oshida et al, 1995). Dans le cas de E hirae, une partie de l'activité de la muramidase M2 est retrouvée dans le surnageant de culture, l'autre partie étant associée aux parois (Kariyama et Shockman, 1992), alors que l'activité de la muramidase M1 est associée en quasi totalité aux cellules.…”

“…La muramidase M1 de E hirae est synthétisée sous forme d'un zymogène de 130 kDa exporté vers la paroi puis clivé en une forme active de 87 kDa (Shockman, 1992). Chez B subtilis au contraire, l'action de protéases extracellulaires inactivent une (ou des) autolysine (s) impliquée(s) dans le renouvellement du peptidoglycane (Jolliffe et al,1980 (Herbold et Glaser, 1975).…”

Bacterial peptidoglycan (murein) hydrolases

“…Turnover products serve as signalling molecules for recognition of bacteria by other organisms and, in some bacteria, for the induction of b-lactamase (Jacobs et al, 1997). Moreover, these hydrolases are also responsible for autolysis induced under certain conditions (Tomasz, 1974(Tomasz, , 1979a(Tomasz, , b, 1980Shockman, 1992;Shockman & Höltje, 1994;Shockman et al, 1996). There are examples of hydrolases for every glycosidic and amide bond in peptidoglycan, although not every specificity is found in every species.…”