Glutamate kinase from Thermotoga maritima: characterization of a thermophilic enzyme for proline biosynthesis.

Glutamate kinase (GK), an enzyme involved in osmoprotection in plants and microorganisms, catalyses the first and controlling step of proline biosynthesis. The proB gene encoding GK was cloned from the hyperthermophilic bacterium Thermotoga maritima and overexpressed in Escherichia coli, and the resulting protein was purified to homogeneity in three simple steps. T. maritima GK behaved as a tetramer, showing maximal activity at 83 degrees C, and was inhibited by ADP and proline. Although T. maritima GK exhibited high amino acid similarity to the mesophilic E. coli GK, it was less dependent of Mg ions and was not aggregated in the presence of proline. Moreover, it displayed a greater thermostability and higher catalytic efficiency than its mesophilic counterpart at elevated temperatures.