Structural characterization, stability and fatty acid-binding properties of two French genetic variants of human serum albumin

Four bisalbuminemic, unrelated persons were found in Bretagne, France, and their variant and normal albumins were isolated by DEAE ion exchange chroma tography, reduced, carboxymethylated and treated with CNBr. Comparative two -dimensional electrophoresis of the CNBr digests showed that three of the v ariants were modified in fragment CB4, whereas the fourth had an abnormal f ragment CB1. These fragments were isolated, digested with trypsin and mappe d by reverse-phase HPLC. Sequencing of altered tryptic peptides showed that the three variants modified in CB4 were caused by the same, previously unr eported, amino acid substitution: Asp(314)--<Val (albumin Brest). The fourt h, however, was a proalbumin variant with the change Arg(-2)-->Cys (albumin Ildut). Both amino acid substitutions can be explained by point mutations in the structural gene: G (A) under bar T-->G (T) under bar T (albumin Bres t) and (C) under bar GT-->(T) under bar GT (albumin Ildut). The proalbumin Ildut is very unstable and already in vivo it is to a large extent cleaved posttranslationally to Arg-Albumin and normal albumin. Furthermore, we obse rved that during a lengthy isolation procedure the remaining proalbumin was changed to Arg-Albumin or proalbumin lacking Arg(-6). In addition, part of normal albumin had lost Asp(1). Gas chromatographic investigations using i solated proteins indicated that albumin Brest has improved in vivo fatty ac id-binding properties, whereas the structural modification(s) of albumin Il dut does not affect fatty acid binding. (C) 1994 Elsevier Science B.. All r ights reserved.