Open AccessSalmonella enterica Serovar Typhimurium Peptidase B Is a Leucyl Aminopeptidase with Specificity for Acidic Amino Acids
Author(s) -
Zacharia Mathew,
Tina M. Knox,
Charles G. Miller
Publication year - 2000
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.182.12.3383-3393.2000
Subject(s) - biology , subfamily , aminopeptidase , biochemistry , peptide sequence , amino acid , salmonella enterica , enzyme , residue (chemistry) , sequence alignment , gene , escherichia coli , leucine
Peptidase B (PepB) ofSalmonella enterica serovar Typhimurium is one of three broad-specificity aminopeptidases found in this organism. We have sequenced thepepB gene and found that it encodes a 427-amino-acid (46.36-kDa) protein, which can be unambiguously assigned to the leucyl aminopeptidase (LAP) structural family. PepB has been overexpressed and purified. The active enzyme shows many similarities to other members of the LAP family: it is a heat-stable (70°C; 20 min) hexameric (∼270-kDa) metallopeptidase with a pH optimum of 8.5 to 9.5. A detailed study of the substrate specificity of the purified protein shows that it differs from other members of the family in its ability to hydrolyze peptides with N-terminal acidic residues. The preferred substrates for PepB are peptides with N-terminal Asp or Glu residues. Comparison of the amino acid sequence of PepB with those of other LAPs leads to the conclusion that PepB is the prototype of a new LAP subfamily with representatives in several other eubacterial species and to the prediction that the members of this family share the ability to hydrolyze peptides with N-terminal acidic residues. Site-directed mutagenesis has been used to show that this specificity appears to be determined by a single Lys residue present in a sequence motif conserved in all members of the subfamily.