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

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.