Streptomyces erythraeus trypsin inactivates α1-antitrypsin

Streptomyces erythraeus trypsin (SET) is a serine protease that is secreted extracellularly by S. erythraeus. We investigated the inhibitory effect of alpha(1)-antitrypsin on the catalytic activity of SET. Intriguingly, we found that SET is not inhibited by alpha(1)-antitrypsin. Our investigations into the molecular mechanism underlying this observation revealed that SET hydrolyzes the Met-Ser bond in the reaction center loop of alpha(1)-antitrypsin. However, SET somehow avoids entrapment by alpha(1)-antitrypsin. We also confirmed that alpha(1)-antitrypsin loses its inhibitory activity after incubation with SET. Thus, our study demonstrates that SET is not only resistant to alpha(1)-antitrypsin but also inactivates alpha(1)-antitrypsin. Structured summary of protein interactions: BT cleaves alpha1 antitrypsin by protease assay (View interaction) alpha1 antitrypsin and BT bind by comigration in non denaturing gel electrophoresis (View interaction) SET cleaves alpha1 antitrypsin by protease assay (View interaction) (C) 2011 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.