Molecular cloning, sequence analysis, and characterization of a new cell wall hydrolase, CwIL, of Bacillus licheniformis

We have cloned a DNA fragment containing the gene for a cell wall hydrolase from Bacillus licheniformis FD0120 into Escherichia coli. Sequencing of the fragment showed the presence of an open reading frame (ORF; designated as cwlL), which is different from the B. licheniformis cell wall hydrolase gene cwlM, and encodes a polypeptide of 360 amino acids with a molecular mass of 38 994. The enzyme purified from the E. coli clone is an N-acetylmuramoyl-l-alanine amidase, which has a M_r value of 41 kDa as determined by SDS-polyacrylamide gel electrophoresis, and is able to digest B. licheniformis, B. subtilis and Micrococcus luteus cell walls. The nucleotide and deduced amino acid sequences of cwlL are very similar to those of ORF3 in the putative operon xpaL1-xpaL2-ORF3 in B. licheniformis MC14. Moreover, the amino acid sequence homology of CwlL with the B. subtilis amidase CwlA indicates two evolutionarily distinguishable regions in CwlL. The sequence homology of CwlL with other cell wall hydrolases and the regulation of cwlL are discussed.