Identification of α1-Antitrypsin Variants in Plasma with the Use of Proteomic Technology

Background: Proteomic technology permits the investigation of genetic metabolic diseases at the level of protein expression. Changes in the expression, polypeptide structure, and posttranslational modification of individual proteins can be detected in complex mixtures of proteins. Methods: We used high-resolution two-dimensional polyacrylamide gel electrophoresis to separate isoforms of plasma proteins and detect abnormalities of mass and/or charge. We confirmed the identity of the separated proteins by in-gel digestion with proteases and N-glycanases and then analyzed the released peptides and glycans by matrix-assisted laser-desorption ionization–time-of-flight mass spectrometry. Results: Complete characterization of the polypeptide sequences and glycosylation of α1-antitrypsin isoforms was achieved in plasma from controls and from patients with three different known α1-antitrypsin deficiencies and congenital disorder of glycosylation type Ia. Conclusions: This study shows that proteomic techniques are a powerful and sensitive means of detecting changes in the amino acid sequence and abnormal posttranslational modifications of specific proteins in a complex biologic matrix.