期刊
JOURNAL OF BIOSCIENCE AND BIOENGINEERING
卷 93, 期 6, 页码 589-594出版社
SOC BIOSCIENCE BIOENGINEERING JAPAN
DOI: 10.1016/S1389-1723(02)80242-0
关键词
peptidase; proline; Lactobacillus; salt-tolerant
X-prolyl dipeptidyl aminopeptidase (X-PDAP) from Lactobacillus helveticus IFO3809 expressed nearly full activity under high salt conditions, such as 2M NaCl. We cloned and sequenced the pepX gene for X-PDAP. The calculated M-r of deduced X-PDAP (803 amino acids) was 90,847 and the protein was distantly related (35 to 44% identity) to known X-PDAPs of Lactobacillus sp. including L. helveticus CNRZ32 (40% identity). Native and recombinant X-PDAP were purified to homogeneity from both L. helvelicus IFO3809 and Escherichia coli DH5alpha harboring the pepX gene on a plasmid, respectively. The native enzyme appeared to be a dimer of 220 kDa, as estimated by gel filtration column chromatography. It hydrolyzed an X-prolyl-linkage, but not prolyl- or X-prolyl-X-peptide bonds, and tolerated up to 2 M NaCl as well as some other chlorides of monovalent cations. Determination of the flanking sequences revealed two divergent genes. The upstream region of the pepX gene encodes oppA gene for a putative oligopeptide permease, while the downstream region encodes tnp gene specifying a possible transposase of the IS3 family. The oppA gene shares a 176 bp-promoter region with pepX in the intergenic region, implying a relationship between this oligopeptide transport system and X-PDAP.
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