Expression and protease characterization of a conserved protein YgjD in .

The glycopeptidase GCP and its homologue proteins are conserved and essential for survival of bacteria. The gene (Glycopeptidase homologue) was cloned from strain SF-1. The gene consisted of 1,017 bp, which encodes a 338 amino acid polypeptide. The nucleotide sequence similarity of the gene with that of FDAARGOS 107 was 95%. The gene also showed similarities of 68%, 67% and 50% with those of , and . The gene was expressed in BL21 (DE3) and the recombinant YgjD was purified by Ni affinity chromatography column. The purified YgjD showed a specific 37 kDa band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and exhibited protease activities of 59,000 units/mg, 53,700 units/mg and 8,100 units/mg, respectively, on N-Acetyl-L-tyrosine ethyl ester monohydrate (ATEE), N-Benzoyl-L-tyrosine ethyl ester (BTEE) and N-Benzoyl-DL-arginine-4-nitroanilide hydrochloride (BAPNA) substrates. When the conserved amino acids of His, Glu and His in the YgjD were replaced with alanine, respectively, the protease activities of the mutants were partly decreased. The two conserved His and His of YgjD were mutated and the protein lost the protease activity, which implied that the two amino acid played very important roles in maintaining its protease activity. The addition of the purified YgjD to the culture medium of strain SF-1 can effectively promote the bacteria growth. These results indicated that the protease activities may be involved in the survival of bacteria.