É-(γ-Glutamyl)lysine cross-links of spore coat proteins and transglutaminase activity in<i>Bacillus subtilis</i>

Abstract

Spores of Bacillus subtilis are resistant to proteolytic enzymes. Some of the spore coat proteins cannot be solubilized even by treatment with strong chemical agents like dithiothreitol. The spore coat has been suggested to possess cross-links between proteins in addition to disulfide bonds. We analyzed B. subtilis spore coat proteins to find specific cross-link structures. We detected ε-(γ-glutamyl)lysine in the spore coat proteins after sequential protease digestion followed by HPLC. We also detected transglutaminase activity in sporulating cells, which incorporated putrescine into N,N′-dimethylcasein. This enzyme was suggested to create ε-(γ-glutamyl)lysine bonds between spore coat proteins.