Functional characterization and crystal structure of thermostable amylase from Thermotoga petrophila, reveals high thermostability and an unusual form of dimerization

Thermostable alpha-amylases have many industrial applications and are therefore continuously explored from novel sources. We present the characterization of a novel putative alpha-amylase gene product (Tp-AmyS) cloned from Thermotoga petrophila. The purified recombinant enzyme is highly thermostable and able to hydrolyze starch into dextrin between 90 and 100 degrees C, with optimum activity at 98 degrees C and pH 8.5. The activity increased in the presence of Rbl +, K1+ and Ca2+ ions, whereas other ions inhibited activity. The crystal structure of Tp-AmyS at 1.7 angstrom resolution showed common features of the GH-13 family, however was apparently found to be a dimer. Several residues from one monomer interacted with a docked acarbose, an inhibitor of Tp-AmyS, in the other monomer, suggesting catalytic cooperativity within the dimer. The most striking feature of the dimer was that it resembled the dimerization of salivary amylase from a previous crystal structure, and thus could be a functional feature of some amylases.