title: Tryptophan-19 of beta-lactoglobulin, the only residue completely conserved in the lipocalin superfamily, is not essential for binding retinol, but relevant to stabilizing bound retinol and maintaining its structure.
abstract: Residue 19 of tryptophan in bovine beta-lactoglobulin (beta-LG) is the only invariant residue throughout the lipocalin superfamily having two characteristic features: binding ability for small hydrophobic molecules and the unique beta-barrel three-dimensional structure. In this study, we investigated whether this strictly conserved Trp-19 of beta-LG would be indispensable for its structure and function such as maintaining the molecular structure and biological activity of beta-LG. Spectroscopic and enzymatic oxidation experiments on retinol bound to W19Y, in which Tyr was substituted for Trp-19, showed that Trp-19 was not critical for this binding, but was important for stably maintaining the environment surrounding retinol and the bound retinol. An using four anti-beta-LG monoclonal antibodies as probes, revealed a structural change in region 20-29, but not in the reverse region of Trp-19. A guanidine hydrochloride-induced unfolding study showed that the conformational stability of W19Y was greatly reduced by 6.9 kcal/mol compared to that of wild-type beta-LG. These facts indicated that Trp-19 is one of the important residues in correctly maintaining the local structure of beta-LG and stably retaining its overall structure, thereby conserving the bound retinol molecule.
authors.affiliation: Department of Agricultural Chemistry, University of Tokyo, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Katakura
authors.forename: M
authors.initials: M
authors.lastname: Totsuka
authors.forename: A
authors.initials: A
authors.lastname: Ametani
authors.forename: S
authors.initials: S
authors.lastname: Kaminogawa
mesh_terms: D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry; D002942:Circular Dichroism; D004795:Enzyme Stability; D007782:Lactoglobulins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D054835:Lipocalin 1; D008969:Molecular Sequence Data; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D012471:Salivary Proteins and Peptides / Q000737:chemistry; D014364:Tryptophan / Q000737:chemistry*; D014801:Vitamin A / Q000737:chemistry* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D007782:Lactoglobulins; D054835:Lipocalin 1; D012471:Salivary Proteins and Peptides; D014801:Vitamin A; D014364:Tryptophan