Glycodelin and beta-lactoglobulin, lipocalins with a high structural similarity, differ in ligand binding properties

Human glycodelin, a lipocalin with a high amino acid similarity to beta-lactoglobulins, appears as various glycoforms with different biological activities in endometrium (glycodelin-A) and seminal plasma (glycodelin-S). We found that the structures of these glycodelins and beta-lactoglobulin are similar. Despite this structural similarity, unlike beta-lactoglobulin, glycodelin-A binds neither retinoic acid nor retinol. It was impossible to detect any endogenous retinoids or steroids in any of the two purified glycodelins. Both their glycoforms share similar thermodynamic parameters of reversible denaturation suggesting that native folding of glycodelin-A and glycodelin-S is not influenced by the differences in glycosylation or by ligand binding.