Site-directed mutagenesis of proposed active-site residues of penicillin-binding protein 5 from Escherichia coli.
Alignment of the amino acid sequence of penicillin-binding protein 5 (PBP5) with the sequences of other members of the family of active-site-serine penicillin-interacting enzymes predicted the residues playing a role in the catalytic mechanism of PBP5. Apart from the active-site (Ser44), Lys47, Ser110-Gly-Asn, Asp175 and Lys213-Thr-Gly were identified as the residues making up the conserved boxes of this protein family. To determine the role of these residues, they were replaced using site-directed mutagenesis. The mutant proteins were assayed for their penicillin-binding capacity and DD-carboxypeptidase activity. The Ser44Cys and the Ser44Gly mutants showed a complete loss of both penicillin-binding capacity and DD-carboxypeptidase activity. The Lys47Arg mutant also lost its DD-carboxypeptidase activity but was able to bind and hydrolyse penicillin, albeit at a considerably reduced rate. Mutants in the Ser110-Gly-Asn fingerprint were affected in both acylation and deacylation upon reaction with penicillin and lost their DD-carboxypeptidase activity with the exception of Asn112Ser and Asn112Thr. The Asp175Asn mutant showed wild-type penicillin-binding but a complete loss of DD-carboxypeptidase activity. Mutants of Lys213 lost both penicillin-binding and DD-carboxypeptidase activity except for Lys213His, which still bound penicillin with a k+2/K' of 0.2% of the wild-type value. Mutation of His216 and Thr217 also had a strong effect on DD-carboxypeptidase activity. Thr217Ser and Thr217Ala showed augmented hydrolysis rates for the penicillin acyl-enzyme. This study reveals the residues in the conserved fingerprints to be very important for both DD-carboxypeptidase activity and penicillin-binding, and confirms them to play crucial roles in catalysis.
BIOSON Research Institute, Department of Biochemistry, University of Groningen, The Netherlands.
M P
MP
van der Linden
L
L
de Haan
O
O
Dideberg
W
W
Keck
D000215:Acylation; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D002268:Carboxypeptidases / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002384:Catalysis; D017124:Conserved Sequence; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D006602:Hexosyltransferases; D007700:Kinetics; D008969:Molecular Sequence Data; D008970:Molecular Weight; D002267:Muramoylpentapeptide Carboxypeptidase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics*; D046915:Penicillin-Binding Proteins; D010406:Penicillins / Q000378:metabolism; D010449:Peptide Mapping; D010458:Peptidyl Transferases; D015183:Restriction Mapping; D016415:Sequence Alignment
D001426:Bacterial Proteins; D002352:Carrier Proteins; D046915:Penicillin-Binding Proteins; D010406:Penicillins; D010458:Peptidyl Transferases; D006602:Hexosyltransferases; D002268:Carboxypeptidases; D002267:Muramoylpentapeptide Carboxypeptidase