Abstract
The bacterial peptidoglycan is the major component of the cell wall which integrity is essential to cell survival. In a previous work, we identified, in the positive-Gram pathogen Streptococcus pneumoniae , a unique protein containing a new putative peptidoglycan hydrolytic domain named PECACE (PEptidoglycan CArbohydrate Cleavage Enzyme). In this study, we characterise the physiological function of this protein called Pmp23 (Pneumococcal Membrane Protein of 23 kDa). A cell wall hydrolytic activity is observed with the recombinant protein. Inactivation of the pmp23 gene in the pneumococcus led to a decreased flocculation, an increased sensitivity to β-lactam antibiotics and morphological alterations affecting the formation and localisation of the division septa. Taken together these observations indicate that Pmp23 is a hydrolase whose function is linked to peptidoglycan metabolism at the septum site.
Highlights
The external bacteria cell wall gives the cellular morphological shape and allows resisting to the intracellular pressure
The probable enzymatic activity deduced from the detailed analysis of the amino-acid sequence suggested that the PECACE domain might proceed through a lytic transglycosylase-type with Slt70 as the paradigm enzyme or goose lysozyme-type cleavage mechanism
PECACE domain was exclusively found in Gram-positive bacteria alone or in association with others domains known to hydrolyse the peptidoglycan
Summary
The external bacteria cell wall gives the cellular morphological shape and allows resisting to the intracellular pressure. The PECACE domain identified in the pneumococcus genome is present in a sequence containing 204 amino acids (predicted molecular weight of 23 kDa), which harbour a short cytoplasmic region, a transmembrane anchor and a large extracellular region; this protein has been named Pmp23 for Pneumococcal Membrane Protein of 23 kDa. We describe here the functional characterization of the Pmp23 protein in the S. pneumoniae R6 strain. Considering the membrane topology of Pmp23 and the putative enzymatic activity deduced from the amino-acid sequence, it appears that the Pmp23 function may differ from the other hydrolases already identified in S. pneumoniae, LytA, LytB, LytC, CbpD and PcsB.
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