Objective: It is a conserved mechanism in bacteria that metalloprotease site-2 protease (S2P) cleaves transmembrane anti-sigma factor to release sequestered sigma factor in response to extracytoplasmic stress. However, the function of site-2 protease homologs in cyanobacteria remains elusive, so we investigated the metalloprotease activity of Slr0643 and Sll0862, the site-2 protease homologs from Synechocystis sp. PCC6803.
Methods: Recombinant Slr0643 and Sll0862 were constructed and overexpressed in Escherichia coli BL21 (CE3). Their protease activities were tested against beta-casein and then resolved on SDS-PAGE.
Results: Results from caseinolytic assay indicated that Slr0643 and Sll0862 have proteolytic activity which is blocked by o-phenanthroline, a metalloprotease inhibitor. These metalloprotease activity of Slr0643 and Sll0862 in vitro provide the foundation for futher analysis of their substrates in vivo.
Conclusion: The site-2 protease homologs in Synechocystis sp. PCC6803 have metalloprotease activity.