3.8 Article

Engineering enhanced thermostability into the Geobacillus pallidus nitrile hydratase

期刊

CURRENT RESEARCH IN STRUCTURAL BIOLOGY
卷 4, 期 -, 页码 256-270

出版社

ELSEVIER
DOI: 10.1016/j.crstbi.2022.07.002

关键词

Nitrile hydratase; Thermostability; Thermophile; Crystal structure; Electrostatic interactions; Protein stability; Protein engineering; Random mutagenesis; Directed evolution

资金

  1. Royal Society (UK)
  2. National Research Foundation (South Africa)
  3. START-Synchrotron Techniques for African Research and Technology (Science and Technology Facilities Council) [ST/R002754/1]
  4. BTS: Department of Integrative Biomedical Sci-ences, Health Sciences Faculty, University of Cape Town

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In this study, mutant enzymes were obtained to enhance the thermostability of nitrile hydratases. The high-resolution crystal structures revealed the importance of salt bridges, hydrogen bonds, and structured water molecules in enhancing enzyme thermostability.
Nitrile hydratases (NHases) are important biocatalysts for the enzymatic conversion of nitriles to industrially-important amides such as acrylamide and nicotinamide. Although thermostability in this enzyme class is generally low, there is not sufficient understanding of its basis for rational enzyme design. The gene expressing the Co-type NHase from the moderate thermophile, Geobacillus pallidus RAPc8 (NRRL B-59396), was subjected to random mutagenesis. Four mutants were selected that were 3 to 15-fold more thermostable than the wild-type NHase, resulting in a 3.4-7.6 kJ/mol increase in the activation energy of thermal inactivation at 63 degrees C. High resolution X-ray crystal structures (1.15-1.80 angstrom) were obtained of the wild-type and four mutant enzymes. Mutant 9E, with a resolution of 1.15 angstrom, is the highest resolution crystal structure obtained for a nitrile hydratase to date. Structural comparisons between the wild-type and mutant enzymes illustrated the importance of salt bridges and hydrogen bonds in enhancing NHase thermostability. These additional interactions variously improved thermostability by increased intra- and inter-subunit interactions, preventing cooperative unfolding of alpha-helices and stabilising loop regions. Some hydrogen bonds were mediated via a water molecule, specifically highlighting the significance of structured water molecules in protein thermostability. Although knowledge of the mutant structures makes it possible to rationalize their behaviour, it would have been challenging to predict in advance that these mutants would be stabilising.

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