Cephalosporinase enzymes

Further, using a combination of X-ray crystallography and mass spectroscopy, Knox et al. [73] has firmly established a central role for Ser-130 in the inhibition of SHV-1 /1-lactamase (class A) by tazobactam. Many additional modifications (Table 3) were carried out on tazobactam with the aim of increasing inhibitory activity against AmpC enzymes, but none of these derivatives (e.g., 13c, 13d, and 13e) had any advantage over tazobactam [74— 77]. Renewed interest in the modification at the C-2 position of sulbactam was developed when scientists from Hoffmann-La Roche disclosed a series of 2/J-alkenyl penam sulfones that possess the ability to simultaneously inactivate both class A penicillinase as well as class C cephalosporinase. Compound... 

Zinc-dependent enzymes [EC 3.5.2.6], including penicillinase and cephalosporinase, with varying specificity in their catalysis of j8-lactam hydrolysis. Some act more readily on penicillins, whereas the catalysis of others is more efficient with cephalosporins. 

There are many beta-lactamases and they can be classified differently by type of substrate, replacement of genes (chromosomes or plasmids), and place of production. A few of these enzymes directly hydrolyze penicillins (penicillinases), others hydrolyze cephalosporins (cephalosporinases), and others extend to a broad spectrum of substrates. A few bacteria have the ability to induce synthesis of beta-lactamase. Synthesis of beta-lactamase, which in a normal condition is suppressed, is induced in the presence of some beta-lactam antibiotics. 

Efforts to overcome the actions of the p-lactamases have led to the development of such p-lactamase inhibitors as clavulanic acid, sulbactam, and tazobactam. They are called suicide inhibitors because they permanently bind when they inactivate p-lactamases. Among the p-lactamase inhibitors, only clavulanic acid is available for oral use. Chemical inhibition of p-lactamases, however, is not a permanent solution to antibiotic resistance, since some p-lactamases are resistant to clavulanic acid, tazobactam, or sulbactam. Enzymes resistant to clavulanic acid include the cephalosporinases produced by Citrobacter spp., Enterobacter spp., and Pseudomonas aeruginosa. 

The class C >8-lactamases include the chromosomal cephalosporinases of Gram-negative bacteria. They are large molecules of approximately 39,000 Da and show no sequence homology with the other classes. The amino-acid residue directly implicated in enzyme action of this class has been identified as serine-80. 

The clinically most important /7-lactamases are regarded as the Grampositive penicillinases, the Richmond-Sykes class I cephalosporinases and the class III plasmid-mediated TEM-1 enzymes. Wherever possible, the... 

The three-dimensional structure of the beta-lactam portion of both penicillins and cephalosporins is sufficiently similar to that of D-alanine-D-alanine (see Fig. 2.4), that the transpeptidase enzyme acts upon the drugs instead of the bacterial polypeptide chain. The enzyme becomes covalently attached to the antibiotic and is then unable to carry out its normal functions such that new cell wall material cannot be produced and the dividing bacterium cannot survive. Unfortunately, the penicillinases and cephalosporinases (now known collectively as beta-lactamases) that have evolved to meet the threat posed by the antibiotics act upon the drugs to destroy their beta-lactam rings so that they can no longer inactivate the transpeptidase enzymes. 

The very broad antibacterial spectrum of imipenem is explicable when its stability is viewed in the presence of P-lactamases mediated by drag-resistance plasmids (mainly penicillinases) and chromosome (primarily cephalosporinases). Imipenem was shown to be stable to enzymes of both types (except P. maltophilia). A comparison of MICs for imipenem, cefazolin, and ampicillin dramatically illustrates the clinical potential for this... 

Bacteria also can destroy /5-lactam antibiotics enzymatically via the actions of /5-lactamases (Figures 44-1 and 44-3). The substrate specificities of some of these enzymes are relatively narrow such enzymes are sometimes referred to as penicillinases or cephalosporinases. Other extended-spectrum enzymes can hydrolyze a variety of /5-lactam antibiotics. 

Beta-lactamases Bacterial enzymes (penicillinases, cephalosporinases) that hydrolyze the beta-lactam ring of certain penicillins and cephalosporins... 

The MALDI-TOF MS assay described above was able to detect the presence of an approximately 39,850-w/z peak, which can be used as an indicator for the presence of the C. ew c(//-derived CMY-2-like group of the acquired AmpC P-lactamases (Papagiannitsis et al. 2014). In addition, the observation of the 39,670 and 38,900-w/z peaks for ACC-4 and DHA-1 enzymes, respectively, indicated that MALDI-TOF MS may discriminate the diverse groups of acquired AmpC-type cephalosporinases (see Fig. 12.4). In addition, the latter method revealed a peak at mIz 383, representing the putative acyl-enzyme complex (complex of CMY-2 P-lactamase with the meropenem molecule). 

Miscellaneous - The enzymes involved in microbial cell wall synthesis " are obvious targets for the design of antimicrobial agents as a number of useful antibiotics act by inhibiting various steps in this process. The modification of penicillinase-and cephalosporinase-resistant semi-synthetic antibiotics could be aided by knowledge of the enzymology of the p-lactamases. ... 

The accumulation of results presented so far suggested that the biosynthesis of the cephalosporins and penicillins was essentially the same in many respects and that, like the penicillins, the cephalosporins were probably derived from a-aminoadipylcysteinylvaline. The cephalosporin producing organisms that have been most studied to date (C. acremonium and S. clavuligerus) both also produce penicillin N. There are, therefore, two possible routes from the tripeptide to the cephem products, one by direct cyclisation of the tripeptide, the other by enzymic ring expansion of penicillin N. The first evidence that penicillin N could be converted enzymically to a cephalosporin was provided by Kohsaka and Demain 289) who demonstrated that lysed protoplasts of C. acremonium could convert penicillin N to another antibiotic or antibiotics which were destroyed by cephalosporinase but not by penicillinase. The product of this cell-free enzymic reaction was characterised as deacetoxycephalosporin C (297) by Yoshida etal. 290). These authors also showed that cell-free... 

Lys-73 Lys-73 apparently plays a significant role in the enhancement of catalytic function. The residue is required for electrostatic stabilization of the anionic tetrahedral intermediate. The Lys-73-Arg mutation in the )8-lactamase I of B. cereus 569/H results in an enzyme with 2-3% of the of the wild-type enzyme (53). A similar site-specific mutation in the class C cephalosporinase of C. freundii GN346 results in an enzyme that retains 35% of the of the wild-type enzyme, whereas nonconservative replacement of the Lys to Thr or Glu results in a nearly complete loss of activity (54). 

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