Skl, a novel choline-binding N-acetylmuramoyl-l-alanine amidase of Streptococcus mitis SK137 containing a CHAP domain

Abstract: The skl gene from Streptococcus mitis SK137 encodes a peptidoglycan hydrolase (Skl) that has been purified and biochemically characterized. Analysis of the degradation products obtained by digestion of pneumococcal cell walls with Skl revealed that this enzyme is an N-acetylmuramoyl-l-alanine amidase (EC 3.5.1.28), showing optimum activity at 30°C and at a pH of 6.5. Skl is a unique member of the choline-binding family of proteins since it contains a cysteine, histidine-dependent amidohydrolases/peptidases (CHAP) domain. The CHAP domain of Skl showed homology to lysins of unknown especificity from a variety of streptococcal prophages. Skl represents the first characterized member of a new subfamily of CHAP-containing choline-binding proteins. [Copyright &y& Elsevier]