Molecular mechanism on a germination cascade reaction of spore-forming bacteria

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In order to elucidate bacterial germination in a molecular level, we studied the activation process of a SleC, a spore cortex-lytic enzyme of Clostridium perfringens which is synthesyzed at an early stage of sporulation as a precursor consisting of 4 domains. After cleavage of an N-terminal presequence and a C-terminal prosequence during spore maturation, inactive proenzyme is converted to active enzyme by processing of a N-terminal prosequence with germination-specific protease GSP during germination. The protease was a cysteine-dependent serine protease and it was suggested that GSP likely is localized with SleC on the exterior of the cortex layer in the dormant spore, a location relevant to the pursuit of a cascade of cortex hydrolytic reaction. SleC was most likely a bifunctional enzyme possessing lytic transglycosylase and N-acetylmuramoyl-L-alanine amidase activities. Cortex hydrolysis was performed by the cooperative action of SleC and SleM, and it was indicated that SleC causes merely small and local changes in the cortex structure, which are necessary before SleM can function. Analysis of muropeptides released during germination revealed that no muramic acid residue in the spore cortex of C. perfringens was substituted with a single L-alanine, which is a major constituent common to spore peptidoglycan of Bacillus species. These results suggest that the mechanism on spore cortex hydrolysis during germination is not conserved between Bacillus species and C. perfringens.