Natural amino acid substitution by single-site
nucleotide polymorphism can become a valuable tool for structure-activity correlations, especially if evidence for association to disease parameters exists. Focusing on the F19Y change in human galectin-8, connected clinically to
rheumatoid arthritis, we here initiate the study of consequences of a single-site substitution in the
carbohydrate recognition domain of this family of cellular effectors. We apply a strategically combined set of structural and cell
biological techniques for comparing properties of the wild-type and variant
proteins. The overall hydrodynamic behavior of the full-length
protein and of the separate N-domain is not noticeably altered, but displacements in the F0 β-strand of the β-sandwich fold in the N-domain are induced, as evidenced by
protein crystallography. Analysis of thermal stability by circular dichroism spectroscopy revealed perceptible differences for the full-length
proteins, pointing to an impact of the substitution beyond the N-domain. In addition, small differences in thermodynamic parameters of
carbohydrate binding are detected. On the level of two types of
tumor cells, characteristics of binding appeared rather similar. In further comparison of the influence on proliferation, the variant proved to be more active as growth regulator in the six tested lines of
neuroblastoma,
erythroleukemia and
colon adenocarcinoma. The seemingly subtle structural change identified here thus has functional implications in vitro, encouraging further analysis in autoimmune regulation and, in a broad context, in work with other natural single-site variants, using the documented combined strategy.
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