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Journal of Bacteriology, May 2000, p. 2536-2543, Vol. 182, No. 9
Department of Microbiology, University of
Illinois at Urbana-Champaign, Urbana, Illinois 61801
Received 22 November 1999/Accepted 31 January 2000
Salmonella enterica serovar Typhimurium peptidase E
(PepE) is an N-terminal Asp-specific dipeptidase. PepE is not inhibited by any of the classical peptidase inhibitors, and its amino acid sequence does not place it in any of the known peptidase structural classes. A comparison of the amino acid sequence of PepE with a number
of related sequences has allowed us to define the amino acid residues
that are strongly conserved in this family. To ensure the validity of
this comparison, we have expressed one of the most distantly related
relatives (Xenopus) in Escherichia coli and
have shown that it is indeed an Asp-specific dipeptidase with properties very similar to those of serovar Typhimurium PepE. The
sequence comparison suggests that PepE is a serine hydrolase. We have
used site-directed mutagenesis to change all of the conserved Ser, His,
and Asp residues and have found that Ser120, His157, and Asp135 are all
required for activity. Conversion of Ser120 to Cys leads to severely
reduced (104-fold) but still detectable activity, and this
activity but not that of the parent is inhibited by thiol reagents;
these results confirm that this residue is likely to be the catalytic
nucleophile. These results suggest that PepE is the prototype of a new
family of serine peptidases. The phylogenetic distribution of the
family is unusual, since representatives are found in eubacteria, an insect (Drosophila), and a vertebrate (Xenopus)
but not in the Archaea or in any of the other eukaryotes
for which genome sequences are available.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Peptidase E, a Peptidase Specific for N-Terminal
Aspartic Dipeptides, Is a Serine Hydrolase
*
Corresponding author. Mailing address: Department of
Microbiology, University of Illinois at Urbana-Champaign, B103 CLSL, 601 S. Goodwin Ave., Urbana, IL 61801. Phone: (217) 244-8418. Fax:
(217) 244-6697. E-mail: charlesm{at}life.uiuc.edu.
Journal of Bacteriology, May 2000, p. 2536-2543, Vol. 182, No. 9
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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