Surface plasmon resonance-based interaction studies reveal competition of Streptomyces lividans type I signal peptidases for binding preproteins

Abstract

Type I signal peptidases (SPases) are responsible for the cleavage of signal peptides from secretory proteins. Streptomyces lividans contains four different SPases, denoted SipW, SipX, SipY and SipZ, having at least some differences in their substrate specificity. In this report in vitro preprotein binding/processing and protein secretion in single SPase mutants was determined to gain more insight into the substrate specificity of the different SPases and the underlying molecular basis. Results indicated that preproteins do not preferentially bind to a particular SPase, suggesting SPase competition for binding preproteins. This observation, together with the fact that each SPase could process each preprotein tested with a similar efficiency in an in vitro assay, suggested that there is no real specificity in substrate binding and processing, and that they are all actively involved in preprotein processing in vivo. Although this seems to be the case for some proteins tested, high-level secretion of others was clearly dependent on only one particular SPase demonstrating clear differences in substrate preference at the in vivo processing level. Hence, these results strongly suggest that there are additional factors other than the cleavage requirements of the enzymes that strongly affect the substrate preference of SPases in vivo.

Function and Evolution of Two Forms of SecDF Homologs in Streptomyces coelicolor

“…As expected, the XlnA activity was dramatically reduced to about 0.1 U/mg dry weight (about 30% of ZJUZ23) in strain ZJU26 with both secD-F and secDF deleted. As S. coelicolor contains at least three xylanases (XlnA, XlnB and XlnC), the XlnA and XlnB are secreted by Sec pathway, whereas the XlnC is secreted by TAT pathway [52]. The basal enzyme activity of total secreted xylanase in S. coelicolor is about 0.1 U/mg dry weight (data not shown).…”

Pseudomonas aeruginosa Possesses Two Putative Type I Signal Peptidases, LepB and PA1303, Each with Distinct Roles in Physiology and Virulence

“…In species with multiple functional SPases, the individual enzymes are usually not essential for viability, and although they can differ in their contributions to the process of secretion, this suggests that they can at least partly complement each other (21,69). Overlapping substrate specificities between different SPases have been commonly observed in Gram-positive bacteria with multiple SPases, while the efficiency of preprotein processing of individual SPases within an organism is known to vary (20,21,62).…”

“…Overlapping substrate specificities between different SPases have been commonly observed in Gram-positive bacteria with multiple SPases, while the efficiency of preprotein processing of individual SPases within an organism is known to vary (20,21,62). A good illustration of a pathogen that has SPases with distinct activities is PAO1, wild-type organism; ⌬PA1303, PA1303 mutant; ⌬PA1303 pHERD26T, PA1303 mutant containing empty vector pHERD26T; ⌬PA1303 pHERD26T-PA1303, PA1303 mutant containing PA1303 in trans (pHERD26T-PA1303).…”