PubMed · 4441544
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K N Nedev, R I Volkov, Iu I Khurgin, D S Chernavskiĭ. [Modeling protein globular structure].. https://pubmed.ncbi.nlm.nih.gov/4441544/
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The effects of polyethylene glycol (PEG) of different molecular weights (400, 2000, 6000, 12,000, 20,000, and 35,000) on the conformational stability and catalytic activity of alpha-chymotrypsin in 60% ethanol were studied. The inactivation caused by the organic solvent was not influenced by PEG 400. However, the PEGs with higher molecular weights up to 35,000 increased the stability of the enzyme, but this alpha-chymotrypsin stabilizing effect was molecular weight-independent. With increase of the molecular weight of PEG, a more stable tertiary structure of the enzyme was observed.
The transformation of a weak hydrogen bond in the free enzyme into a low-barrier hydrogen bond (LBHB) in the tetrahedral intermediate has been suggested as an important factor facilitating catalysis in serine proteases. In this work, we examine the structure of the H-bond in the Asp102-His57 diad of serine proteases in the free enzyme and in a covalent tetrahedral complex (TC) with a trifluoromethylketone inhibitor. We apply ab initio quantum mechanical calculations to models consisting of a large molecular fragment of the enzyme active site, and the combined effect of the rest of the protein body and the solvation by surrounding bulk water was simulated by a self-consistent reaction field method in our novel QM/SCRF(VS) approach. Potential profiles of adiabatic proton transfer in the Asp102-His57 diad in these model systems were calculated. We conclude that the hydrogen bond in both the free enzyme and in the enzyme-inhibitor TC is a strong ionic asymmetric one-well hydrogen bond, in contrast to a previous suggestion that it is a weak H-bond in the former and a double-well LBHB in the latter.
We have demonstrated that thiol-bearing analogues of alpha-chymotrysin (alpha-CT) substrates such as (S)-(1-benzyl-2-thiolethyl)-carbamic acid, benzyl ester (3) inhibits alpha-CT, a prototypical serine protease, in the presence of Zn(II) ion. They constitute a novel class of small molecule inhibitors for alpha-CT believed to inhibit the enzyme by forming a ternary complex consisting of alpha-CT, Zn(II) ion, and the inhibitor.