Structural highlights
Function[SPPA_BACSU] Digestion of cleaved signal peptides (By similarity). Required for efficient processing of precursors under conditions of hyper-secretion. Publication Abstract from PubMedBacterial signal peptide peptidase A (SppA) is a membrane-bound enzyme that utilizes a serine/lysine catalytic dyad mechanism to cleave remnant signal peptides within the cellular membrane. Bacillus subtilis SppA (SppABS) oligomerizes into a homo-octameric dome-shaped complex with eight active sites, located at the interface between each protomer. In this study, we show that SppABS self-processes its own C-termini. We have determined the crystal structure of a proteolytically stable fragment of SppABSK199A that has its C-terminal peptide bound in each of the eight active sites, creating a perfect circle of peptides. Substrate specificity pockets S1, S3, and S2' are identified and accommodate C-terminal residues Tyr331, Met329, and Tyr333, respectively. Tyr331 at the P1 position is conserved among most Bacillus species. The structure reveals that the C-terminus binds within the substrate-binding grooves in an antiparallel beta-sheet fashion. We show, by C-terminal truncations, that the C-terminus is not essential for oligomeric assembly. Kinetic analysis shows that a synthetic peptide corresponding to the C-terminus of SppABS competes with a fluorometric peptide substrate for the SppABS active site. A model is proposed for how the C-termini of SppA may function in the regulation of this membrane-bound self-compartmentalized protease. Structure of signal peptide peptidase A with C-termini bound in the active sites: insights into specificity, self-processing, and regulation.,Nam SE, Paetzel M Biochemistry. 2013 Dec 10;52(49):8811-22. doi: 10.1021/bi4011489. Epub 2013 Nov, 25. PMID:24228759[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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