Protein and gene structure analysis of an albumin genetic variant: proalbumin Wu Yang (–2 Arg → His)

Abstract

An electrophoretically slow genetic variant of human serum albumin was isolated from a patient with bis-albuminemia in Xin Jiang who originated in the province of He Nan, county Wu Yang. Based on the FPLC-CNBr peptide profiles of the variant and normal albumins, the mutated CNBr peptide of the variant was found. Both the mutated and corresponding normal CNBr peptides were further subjected to trypsin digestion. An additional peptide peak from the mutated CNBr peptide was found in the HPLC mapping. The amino acid sequence of this peptide was determined to be Gly-Val-Phe-His-Arg corresponding to the fragment of albumin propeptide from position -5 to -1 with an -2 Arg-->His mutation. The N-terminal sequence of the mutated CNBr peptide was also determined to be Arg-Gly-Val-Phe-His*-Arg-Asp-Ala-His-Lys-, namely the N-terminal part of the mutated proalbumin. According to the known genomic structure of proalbumin, the gene fragments neighbouring the propeptide DNA sequences of the normal and variant albumins were amplified in vitro by polymerase chain reaction. The PCR products with 390 bp were then cloned into M13 vector, respectively. The nucleotide sequence analyses demonstrated that the codon CGT for -2 Arg was mutated to CAT for His. Thus, the point substitution was confirmed both at protein and gene levels. The above genetic variant of albumin was named proalbumin Wu Yang (-2 Arg-->His) being the first instance of the Lille type found in China.