Cloning and expression of gene fragments encoding the choline-binding domain of pneumococcal murein hydrolases.

The cloning in Escherichia coli of the 3' moieties of the lytA and cpl-1 genes is described, coding for the C-terminal regions of the lytic amidase of Streptococcus pneumoniae and the phage Cp-1 lysozyme, respectively. The truncated genes were overexpressed in E. coli and the purified polypeptides showed a great affinity for choline, although they were devoid of cell wall-degrading activity. Biochemical and circular dichroism analyses indicated that these are the domains responsible for the specific recognition of the choline-containing pneumococcal cell walls by the lytic enzymes. The data presented here suggested that these choline-binding domains can function independently of their catalytic domains.