Nucleotide sequence of the PSE-4 carbenicillinase gene and correlations with the Staphylococcus aureus PC1 beta-lactamase crystal structure.

The nucleotide sequence of the PSE-4 beta-lactamase gene from Pseudomonas aeruginosa strain Dalgleish has been determined. The structural gene encodes a polypeptide product of 252 amino acids with an estimated molecular mass of 29,246 Da for the mature form of the protein. The PSE-4 gene has limited homology with other beta-lactamases at the DNA level. An alignment of all known class A beta-lactamases permitted as to identify specific residues important for enzyme structure and function. To confirm observations based on the linear sequences, we designed a new molecular model for PSE-4 beta-lactamase based on x-ray data from the Staphylococcus aureus PC1 beta-lactamase at 2.0-A resolution. The structural similarities between PSE-4 and class A beta-lactamases are more extensive than indicated by earlier biochemical studies. The combined structural and sequence information now available for a series of beta-lactamases identifies conserved residues in these molecules, giving insight of their divergence and ancestry. Analysis of the PSE-4 flanking DNA sequences revealed an integration site common to antibiotic resistance genes inserted into transposons of the Tn21 family with the target integration sequence AAGTT.