Structural properties of human glycodelin A in water and in water-alcohol mixtures:: a comparison with bovine β-lactoglobulin A

Human glycodelin A (GdA) is a glycoprotein that is highly homologous to bovine P-lactoglobulin A (beta-LgA) because the amino acid sequences are 50-60% identical. The structural characteristics of human GdA and beta-LgA were compared in water and 2-propanol/water solutions. Circular dichroism spectra reveal that in water the two proteins have a very similar beta-sheet secondary structure. In the presence of 2-propanol/water mixtures (up to 50% v/v) the a-helix structure of both proteins increases. A further increase in the alcohol percentage of the solvent (up to 80% v/v 2-propanol) causes the formation of a new folded tertiary structure containing mainly beta-sheet features. Synchrotron radiation small angle X-ray scattering indicates that, in a neutral pH aqueous solution, GdA is a dimer. Its radius of gyration value (R-g), 25.1 +/- 0.4 Angstrom, is greater than that of beta-LgA (21.1 +/- 0.3 Angstrom), probably because of the contribution of polysaccharides bound to Asn-28 and Asn-63 residues of GdA. Conversely, small angle X-ray scattering and gel permeation chromatography data on GdA in 2-propanol have revealed a massive aggregation of the protein. (C) 1999 Published by Elsevier Science B.V. All rights reserved.