Haptoglobin Gene Subtyping by Restriction Enzyme Analysis

[摘要] Haptoglobin is an acute-phase protein synthesized by the liver in response to inflammatory cytokines (1)(2). Its major function is to form a stable complex with free hemoglobin released from old red blood cells or during episodes of hemolysis, thus preventing iron loss and renal damage (1)(2). Haptoglobin consists of two chains, the α-chain and the β-chain, which are derived from a single polypeptide after proteolytic cleavage (3). The α-chain exists in two major forms, the α1-chain and the α2-chain, which are characterized by the presence (α2-chain) or absence (α1-chain) of a direct repeat of 63 amino acids (1)(2)(3). The structural heterogeneity of the α-chain is the result of an intragenic duplication of ∼1700 bp (3). The 1700-bp sequence of the Hp 1 allele and the upstream 1700-bp sequence of the Hp 2 allele contain exons 3 and 4, and the downstream 1700-bp sequence of the Hp 2 allele carries exons 5 and 6 (3). Three principal genotypes, Hp 1-1, Hp 2-1, and Hp 2-2, result from the haptoglobin gene polymorphism, and we have previously established a technique, based on PCR, for genotype determination (4).Two common sequence versions of the 1700-bp unit exist, which are correlated with the presence of amino acids Asp-Lys (version F) or Asn-Glu (version S) at amino acid positions 52 and 53 in the α1- and α2-chains of haptoglobin and amino acid positions 111 and 112 in the α2-chain (3)(5). Additional differences between the nucleotide sequences of the F-specific and S-specific 1700-bp units occur, including point mutations and small insertions or deletions; however, these differences have no effect on the amino acid sequence (3)(5). Conventional assays for haptoglobin subtyping …

[学科分类] 过敏症与临床免疫学