Psychrophilic enzymes: Hot topics in cold adaptation

More than three-quarters of the Earth's surface is occupied by cold ecosystems, including the ocean depths, and polar and alpine regions. These permanently cold environments have been successfully colonized by a class of extremophilic microorganisms that are known as psychrophiles (which literally means cold-loving). The ability to thrive at temperatures that are close to, or below, the freezing point of water requires a vast array of adaptations to maintain the metabolic rates and sustained growth compatible with life in these severe environmental conditions

Identification and characterization of an unusual metallo-beta-lactamase from Serratia proteamaculans

Metallo-beta-lactamases (MBLs) are a family of metalloenzymes that are capable of hydrolyzing beta-lactam antibiotics and are an important means by which bacterial pathogens use to inactivate antibiotics. A database search of the available amino acid sequences from Serratia proteamaculans indicates the presence of an unusual MBL. A full length amino acid sequence alignment indicates overall homology to B3-type MBLs, but also suggests considerable variations in the active site, notably among residues that are relevant to metal ion binding. Steady-state kinetic measurements further indicate functional differences and identify two relevant pK (a) values for catalysis (3.8 for the enzyme-substrate complex and 7.8 for the free enzyme) and a preference for penams with modest reactivity towards some cephalosporins. An analysis of the metal ion content indicates the presence of only one zinc ion per active site in the resting enzyme. In contrast, kinetic data suggest that the enzyme may operate as a binuclear enzyme, and it is thus proposed that a catalytically active di-Zn2+ center is formed only once the substrate is present