Structural and thermodynamic analysis of the binding of solvent at internal sites in T4 lysozyme

J. Xu et al., Structural and thermodynamic analysis of the binding of solvent at internal sites in T4 lysozyme, PROTEIN SCI, 10(5), 2001, pp. 1067-1078
Citations number
Categorie Soggetti
Biochemistry & Biophysics
Journal title
ISSN journal
0961-8368 → ACNP
Year of publication
1067 - 1078
SICI code
To investigate the structural and thermodynamic basis of the binding of sol vent at internal sites within proteins a number of mutations were construct ed in T4 lysozyme. Some of these were designed to introduce new solvent-bin ding sites. Others were intended to displace solvent from preexisting sites . In one case Val-149 was replaced with alanine, serine, cysteine, threonin e, isoleucine, and glycine. Crystallographic analysis shows that, with the exception of isoleucine, each of these substitutions results in the binding of solvent at a polar site that is sterically blocked in the wild-type enz yme. Mutations designed to perturb or displace a solvent molecule present i n the native enzyme included the replacement of Thr-152 with alanine, serin e, cysteine, valine, and isoleucine. Although the solvent molecule was move d in some cases by up to 1.7 Angstrom, in no case was it completely removed from the folded protein. The results suggest that hydrogen bonds from the protein to bound solvent are energy neutral. The binding of solvent to inte rnal sites within proteins also appears to be energy neutral except insofar as the bound solvent may prevent a loss of energy due to potential hydroge n bonding groups that would otherwise be unsatisfied. The introduction of a solvent-binding site appears to require not only a cavity to accommodate t he water molecule but also the presence of polar groups to help satisfy its hydrogen-bonding potential. It may be easier to design a site to accommoda te two or more water molecules rather than one as the solvent molecules can then hydrogen-bond to each other. For similar reasons it is often difficul t to design a point mutation that will displace a single solvent molecule f rom the core of a protein.