Posttranslational processing of the xylanase Xys1L from Streptomyces halstedii JM8 is carried out by secreted serine proteases

Abstract

The xylanase Xys1L fromStreptomyces halstediiJM8 is known to be processed extracellularly, to produce a protein of 33·7 kDa, Xys1S, that retains catalytic activity but not its cellulose-binding capacity. This paper demonstrates that at least five serine proteases isolated fromStreptomycesspp. have the ability to process the xylanase Xys1L. The genes of two of these extracellular serine proteases, denominated SpB and SpC, were cloned fromStreptomyces lividans66 (a strain commonly used as a host for protein secretion), sequenced, and overexpressed inS. lividans; both purified proteases were able to process Xys1Lin vitro. Three other previously reported purifiedStreptomycesserine proteases, SAM-P20, SAM-P26 and SAM-P45, also processed Xys1Lin vitro. The involvement of serine proteases in xylanase processing-degradationin vivowas demonstrated by co-expression of the xylanase gene (xysA) and the gene encoding the serine protease inhibitor (SLPI) fromS. lividans. Co-expression prevented processing and degradation of Xys1L and resulted in a threefold increase in the xylanase activity present in the culture supernatant. SpB and SpC also have the capacity to process other secreted proteins such as p40, a cellulose-binding protein fromS. halstediiJM8, but do not have any clear effect on other secreted proteins such as amylase (Amy) fromStreptomyces griseusand xylanase Xyl30 fromStreptomyces avermitilis.