Words similar to β-lactamase
Example sentences for: β-lactamase
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S. maltophilia is an important pathogen in nosocomial infections of immunocompromised patients suffering from cancer, cystic fibrosis, drug addition, AIDS and in patients with organ transplants and on dialysis [ 30 31 32 ] . This organism is inherently resistant to most antibiotics due to its low outer membrane permeability [ 33 ] and to β-lactam containing antibiotics due to the production of a chromosomally expressed group 2e β-lactamase (L2) and a group 3c β-lactamase (L1) [ 34 35 ] . L1 has been cloned, over-expressed, and partially characterized by kinetic and crystallographic studies [ 36 37 ] . The enzyme exists as a homotetramer of ca. 118 kDa in solution and in the crystalline state.
There are over 300 distinct β-lactamases known, and these enzymes have been grouped by a number of classification schemes [ 8 9 10 11 12 13 14 15 ] . For example, Bush has developed a scheme, based on the enzymes' molecular properties, that has four distinct β-lactamase groups [ 10 15 ] . One of the more alarming groups are the Bush group 3 enzymes, which are Zn(II) dependent enzymes that hydrolyze nearly all known β-lactam containing antibiotics and for which there are no or very few known clinical inhibitors [ 9 14 16 17 18 19 ] . The metallo-β-lactamases have been further divided by Bush into subgroups based on amino acid sequence identity: the Ba enzymes share a >23% sequence identity, require 2 Zn(II) ions for full activity, prefer penicillins and cephalosporins as substrates, and are represented by metallo-β-lactamase CcrA from Bacteroides fragilis, the Bb enzymes share a 11% sequence identity with the Ba enzymes, require only 1 Zn(II) ion for full activity, prefer carbapenems as substrates, and are represented by the metallo-β-lactamase imiS from Aeromonas sobria, and the Bc enzymes have only 9 conserved residues with the other metallo-β-lactamases, require 2 Zn(II) ions for activity, contain a different metal binding motif than the other metallo-β-lactamases, prefer penicillins as substrates, and are represented by the metallo-β-lactamase L1 from Stenotrophomonas maltophilia [ 9 ] . A similar grouping scheme (B1, B2, and B3) based on structural properties of the metallo-β-lactamases has recently been offered [ 41 ] . The diversity of the group 3 β-lactamases is best exemplified by the enzymes' vastly differing efficacies towards non-clinical inhibitors; these differences predict that one inhibitor may not inhibit all metallo-β-lactamases [ 18 20 21 22 23 24 25 26 27 28 29 ] . To combat this problem, we are characterizing a metallo-β-lactamase from each of the subgroups in an effort to identify a common structural or mechanistic aspect of the enzymes that can be targeted for the generation of an inhibitor.
To combat these enzymes, β-lactamase inhibitors such as clavulanic acid, sulbactam, and tazobactam have been given in combination with a β-lactam containing antibiotic to treat bacterial infections [ 52 ] . One class of β-lactamases that are particularly unaffected by the known β-lactamase inhibitors and have been shown to hydrolyze almost all known β-lactam containing antibiotics including late generation carbapenems at high rates are the metallo-β-lactamases [ 14 15 16 17 18 19 ] . Although there are no reports of metallo-β-lactamases isolated from major pathogens [ 51 53 ] , these enzymes are produced by pathogens such as B. fragilis, S. maltophilia, and P. aeruginosa.
L1's preference for penicillins and carbapenems over cephalosporins, as exemplified by the k cat values, is in agreement with previous studies and supports L1's placement in the β-lactamase 3c family [ 9 ] .
Finally, the β-lactamase fold consists of two subdomains of the β4-α-β-α topology whose β sheets are sandwiched against each other; in structural terms, these domains are completely different from the TIM-barrel, with which the ORF program matched the MJ0301 structural prediction.
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