Enzymes from Cold‐Adapted Microorganisms — The Class C β‐lactamase from the Antarctic Psychrophile Psychrobacter Immobilis A5

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Abstract
A heat‐labile β‐lactamase has been purified from culture supernatants of Psychrobacter immobilis A5 grown at 4°C and the corresponding chromosomal ampC gene has been cloned and sequenced. All structural and kinetic properties clearly relate this enzyme to class C β‐lactamases. The kinetic parameters of P. immobilisβ‐lactamase for the hydrolysis of some β‐lactam antibiotics are in the same range as the values recorded for the highly specialized cephalosporinases from pathogenic mesophilic bacteria. By contrast, the enzyme displays a low apparent optimum temperature of activity and a reduced thermal stability. Structural factors responsible for the latter property were analysed from the three‐dimensional structure built by homology modelling. The deletion of proline residues in loops, the low number of arginine‐mediated H‐bonds and aromatic‐aromatic interactions, the lower global hydrophobicity and the improved solvent interactions through additional surface acidic residues appear to be the main determinants of the enzyme flexibility.