Structure and Dynamics of a Thermostable Alcohol Dehydrogenase from the Antarctic Psychrophile Moraxella sp. TAE123

摘要

The structure of a recombinant (His-tagged at C-terminus) alcohol dehydrogenase (Mo ADH) from the cold-adapted bacterium Moraxella sp. TAE123 has been refined with X-ray diffraction data extending to 1.9 ? resolution. The enzyme assumes a homo-tetrameric structure. Each subunit comprises two distinct structural domains: the catalytic domain (residues 1–150 and 288–340/345) and the nucleotide-binding domain (residues 151–287). There are two Zn~(2+) ions in each protein subunit. Two additional zinc ions have been found in the crystal structure between symmetry-related subunits. The structure has been compared with those of homologous enzymes from Geobacillus stearothermophilus (Gs ADH), Escherichia coli (Ec ADH), and Thermus sp. ATN1 (Th ADH) that thrive in environments of diverse temperatures. Unexpectedly, Mo ADH has been found active from 10 to at least 53 °C and unfolds at 89 °C according to circular dichroism spectropolarimetry data. Mo ADH with substrate ethanol exhibits a small value of activation enthalpy ΔH ~(?) of 30 kJ mol~(–1). Molecular dynamics simulations for single subunits of the closely homologous enzymes Mo ADH and Gs ADH performed at 280, 310, and 340 K showed enhanced wide-ranging mobility of Mo ADH at high temperatures and generally lower but more distinct and localized mobility for Gs ADH. Principal component analysis of the fluctuations of both ADHs resulted in a prominent open–close transition of the structural domains mainly at 280 K for Mo ADH and 340 K for Gs ADH. In conclusion, Mo ADH is a very thermostable, cold-adapted enzyme and the small value of activation enthalpy allows the enzyme to function adequately at low temperatures.