A glutamic acid to lysine change in the Z variant of human α1-antitrypsin is associated with a failure to secrete the protein from synthesising cells. The block in export of the protein may be caused either by the loss of an acidic residue or the introduction of a basic one at this point in the polypeptide chain. Site-directed mutagenesis has been used to construct novel α1-antitrypsin mutants which show that the side chain interactions from Glu-342 are not obligatory for protein export and it is rather the introduction of a basic residue at this point which produces the intracellular accumulation of the protein.
