title: The cataract-associated V41M mutant of human γS-crystallin shows specific structural changes that directly enhance local surface hydrophobicity.
abstract: The major crystallins expressed in the human lens are γS-, γC- and γD-crystallins. Several mutations in γS-crystallin are associated with hereditary cataracts, one of which involves the substitution of a highly conserved Valine at position 41 to Methionine. According to a recent report, the mutant protein, V41M, shows lower stability and increased surface hydrophobicity compared to the wild-type, and a propensity for self-aggregation. Here we address the structural differences between the two proteins, with residue-level specificity using NMR spectroscopy. Based on the structural model of the mutant protein, our results clearly show that the mutation creates a major local perturbation almost at the junction of the first and second "Greek-key" motifs in the N-terminal domain. A larger section of the second motif (residues 44-86) appears to be mainly affected. Based on the sizeable chemical shift of the imino proton of the indole side-chain of Trp46 in V41M, we suggest that the sulphur atom of Met41 is involved in an S-π interaction with Trp46. This interaction would bring the last β-strand of the first "Greek-key" motif closer to the first β-strand of the second motif. This appears to lead to a domino effect, towards both the N- and C-terminal ends, even as it decays off substantially beyond the domain interface. During this process discreet hydrophobic surface patches are created, as revealed by ANS-binding. Such changes would not affect the secondary structure or cause a major change in the tertiary structure, but can lead to self-aggregation or aberrant binding interactions of the mutant protein in vivo, and lead to lens opacity or cataract.
authors.affiliation: Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, United States.
authors.forename: Somireddy Venkata
authors.initials: SV
authors.lastname: Bharat
authors.affiliation: Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, United States.
authors.forename: Alexander
authors.initials: A
authors.lastname: Shekhtman
authors.affiliation: Department of Chemistry, University at Albany, State University of New York, Albany, NY 12222, United States. Electronic address: jpande@albany.edu.
authors.forename: Jayanti
authors.initials: J
authors.lastname: Pande
mesh_terms: D000577:Amides / Q000737:chemistry; D019943:Amino Acid Substitution; D002386:Cataract / Q000378:metabolism*; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008715:Methionine / Q000737:chemistry / Q000235:genetics; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular; D017434:Protein Structure, Tertiary; D014633:Valine / Q000737:chemistry / Q000235:genetics; D038222:gamma-Crystallins / Q000737:chemistry* / Q000235:genetics
chemical_list: D000577:Amides; D038222:gamma-Crystallins; C077648:CRYGS protein, human; D008715:Methionine; D014633:Valine
keywords: 4,4′-Dianilino-1,1′-binaphthyl-5,5′disulfonic acid; 8-Anilinonaphthalene-1-sulfonic acid; ANS; CSP; Cataract; Chemical shift perturbation; Crystallin; HGS; HSQC; Human γS crystallin; Hydrophobicity; NMR spectroscopy; S–pi interactions; V41M; bis-ANS; heteronuclear single quantum coherence; the Val41Met mutant of human γS crystallin