Characterization of the sequence of the normal alpha-1-antitrypsin M3 allele and function of the M3 protein.
Alpha-1-antitrypsin (alpha 1AT), a highly pleomorphic 52 kD glycoprotein, functions chiefly as the major inhibitor of neutrophil elastase. Of the known alpha 1AT variants, greater than 95% in the U.S. Caucasian population are those of the "normal" M family, including M1(Ala213), M1(Val213), M2 and M3, with M3 the least common of the group. Quantification of the functional capacity of the M3 protein as an inhibitor of neutrophil elastase demonstrated a Kassociation for neutrophil elastase of 10.1 +/- 1.5 x 10(6) M-1 s-1, a value comparable to the common normal M1(Val213) alpha 1AT. To define the nucleotide sequence of the M3 gene, the five coding exons of the alpha 1AT gene of an M3 homozygote were amplified by the polymerase chain reaction and cloned into the plasmid vector pUC19. Sequence analysis demonstrated that the alpha 1AT M3 gene differs from the alpha 1AT M1(Val213) gene by a single base substitution (Glu376 GAA----Asp376 GAC) and from the alpha 1AT M2 gene by a single base substitution (His101 CAT----Arg101 CGT). To establish the consistency of the alpha 1AT M3 genotype among individuals identified by isoelectric focusing of serum to have the M3 phenotype, analysis of genomic DNA of 16 individuals by means of allele-specific amplification revealed that residues 101 and 376 were Arg and Asp, respectively, in all M3 alleles, while residue 101 was His in all M2 alleles and residue 376 was Glu in all M1 alleles.(ABSTRACT TRUNCATED AT 250 WORDS)