Lung polymers in Z alpha1-antitrypsin deficiency-related emphysema.
Patients with alpha1-antitrypsin (alpha1-AT) deficiency are at risk of developing early-onset panlobular basal emphysema, which has been attributed to uncontrolled proteolytic activity within the lung. Severe genetic deficiency of alpha1-AT is most commonly due to the Z mutation (342Glu--> Lys), which results in a block in alpha1-AT processing within the endoplasmic reticulum of hepatocytes. The retained alpha1-AT forms inclusions, which are associated with neonatal hepatitis, juvenile cirrhosis, and hepatocellular carcinoma. Our recent studies have shown that the accumulation of alpha1-AT is due to the Z mutation perturbing the structure of alpha1-AT to allow polymer formation, with a unique linkage between the reactive center loop of one alpha1-AT molecule and the A beta-pleated sheet of a second. The detection of loop-sheet polymers and other conformations of alpha1-AT in the lungs of patients with emphysema has been technically difficult. We show here that transverse urea-gradient-gel (TUG) electrophoresis and Western blot analysis may be used to characterize conformations of alpha1-AT in dilute samples of bronchoalveolar lavage fluid (BALF). This technique was used to demonstrate loop-sheet polymers in the lungs of patients with Z alpha1-AT-deficiency-related emphysema. Polymers were the predominant conformational form of alpha1-AT in BALF from the lungs of two of five Z homozygotes with emphysema, but were not detectable in any of 13 MM, MS, or MZ alpha1-AT controls. Because alpha1-AT loop-sheet polymers are inactive as proteinase inhibitors, this novel conformational transition will further reduce the levels of functional proteinase inhibitor in the lungs of the Z alpha1-AT homozygote, and so exacerbate tissue damage.
Elliott
P R
PR
Departments of Medicine and Haematology, University of Cambridge, and Chest Medical Unit, Papworth Hospital, Cambridge, United Kingdom.
Bilton
D
D
Lomas
D A
DA
D001992:Bronchoalveolar Lavage Fluid / Q000737:chemistry; D004586:Electrophoresis / Q000379:methods; D004646:Emphysema / Q000378:metabolism*; D006801:Humans; D011108:Polymers; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D000515:alpha 1-Antitrypsin / Q000737:chemistry*; D019896:alpha 1-Antitrypsin Deficiency / Q000378:metabolism*
D011108:Polymers; D000515:alpha 1-Antitrypsin