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Comparison of the three-dimensional structure of hyperthermophilic and mesophilic β-glycosidases shows differences in secondary
structure composition. The enzymes from hyperthermophilic archaea have a significantly larger number of β-strands arranged
in supernumerary β-sheets compared to mesophilic enzymes from bacteria and other organisms. Amino acid replacements designed
to alter the structure of the supernumerary β-strands were introduced by site directed mutagenesis into the sequence encoding
the β-glycosidase from Sulfolobus solfataricus. Most of the replacements caused almost complete loss of activity but some yielded enzyme variants whose activities were
affected specifically at higher temperatures. Far-UV CD spectra recorded as a function of temperature for both wild type β-glycosidase
and mutant V349G, one of the mutants with reduced activity at higher temperatures, were similar, showing that the protein
structure of the mutant was stable at the highest temperatures assayed. The properties of mutant V349G show a difference between
thermostability (stability of the protein structure at high temperatures) and thermophilicity (optimal activity at high temperatures). 相似文献
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