Abstract
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THE past decade has seen an alarming worldwide increase in resistance to ��-lactam antibiotics among many pathogenic bacteria1, which is due mainly to plasmid- or chromosomally encoded p-lactamases that specifically cleave penicillin and cephalosporins, rendering them inactive. There is therefore a need to develop new strategies in the design of effective inhibitors of ��-lactamase. All the small-molecule inhibitors in clinical use are not very effective and are rapidly degraded2,3. Furthermore, newly characterized mutants of the plasmid-mediated ��-lactamase TEM-1 are highly resistant to these small-molecule inhibitors, including clavulanic acid and tazobactam4. It has been shown that Streptomyces clavuligerus produces an ��-lactamase inhibitory protein (BLIP; MT 17.5 K)5. Here we present data defining BLIP as the most effective known inhibitor of a variety of ��-lactamase, with Ki values in the subnanomolar to picomolar range. To identify those features in BLIP that make it such a potent inhibitor, we have determined its molecular structure at 2.1 �� resolution. BLIP is a relatively flat molecule with a unique fold, comprising a tandem repeat of a 76-amino-acid domain. Each domain consists of a helix-loop-helix motif that packs against a four-stranded antiparallel ��-sheet (Fig. la). To our knowledge, BLIP is the first example of a protein inhibitor having two similarly folded domains that interact with and inhibit a single target enzyme. �� 1994 Nature Publishing Group.