title: Solution properties of γ-crystallins: hydration of fish and mammal γ-crystallins.
abstract: Lens γ crystallins are found at the highest protein concentration of any tissue, ranging from 300 mg/mL in some mammals to over 1000 mg/mL in fish. Such high concentrations are necessary for the refraction of light, but impose extreme requirements for protein stability and solubility. γ-crystallins, small stable monomeric proteins, are particularly associated with the lowest hydration regions of the lens. Here, we examine the solvation of selected γ-crystallins from mammals (human γD and mouse γS) and fish (zebrafish γM2b and γM7). The thermodynamic water binding coefficient B₁ could be probed by sucrose expulsion, and the hydrodynamic hydration shell of tightly bound water was probed by translational diffusion and structure-based hydrodynamic boundary element modeling. While the amount of tightly bound water of human γD was consistent with that of average proteins, the water binding of mouse γS was found to be relatively low. γM2b and γM7 crystallins were found to exhibit extremely low degrees hydration, consistent with their role in the fish lens. γM crystallins have a very high methionine content, in some species up to 15%. Structure-based modeling of hydration in γM7 crystallin suggests low hydration is associated with the large number of surface methionine residues, likely in adaptation to the extremely high concentration and low hydration environment in fish lenses. Overall, the degree of hydration appears to balance stability and tissue density requirements required to produce and maintain the optical properties of the lens in different vertebrate species.
authors.affiliation: Dynamics of Macromolecular Assembly Section, Laboratory of Cellular Imaging and Macromolecular Biophysics, National Institute of Biomedical Imaging and Bioengineering, Bethesda, Maryland, 20892.
authors.forename: Huaying
authors.initials: H
authors.lastname: Zhao
authors.forename: Yingwei
authors.initials: Y
authors.lastname: Chen
authors.forename: Lenka
authors.initials: L
authors.lastname: Rezabkova
authors.forename: Zhengrong
authors.initials: Z
authors.lastname: Wu
authors.forename: Graeme
authors.initials: G
authors.lastname: Wistow
authors.forename: Peter
authors.initials: P
authors.lastname: Schuck
mesh_terms: D000818:Animals; D005136:Eye Proteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D057446:Hydrodynamics; D007908:Lens, Crystalline / Q000378:metabolism*; D008715:Methionine / Q000032:analysis; D051379:Mice; D008958:Models, Molecular; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D055550:Protein Stability; D012995:Solubility; D012996:Solutions; D013816:Thermodynamics; D015027:Zebrafish; D029961:Zebrafish Proteins / Q000737:chemistry* / Q000378:metabolism; D038222:gamma-Crystallins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D005136:Eye Proteins; D012996:Solutions; D029961:Zebrafish Proteins; D038222:gamma-Crystallins; D008715:Methionine
keywords: crystallin; hydrodynamic modeling; protein hydration; protein hydrodynamics; protein interactions