title: Chitin accelerates activation of a novel haloarchaeal serine protease that deproteinizes chitin-containing biomass.
abstract: The haloarchaeon Natrinema sp. strain J7-2 has the ability to degrade chitin, and its genome harbors a chitin metabolism-related gene cluster that contains a halolysin gene, sptC. The sptC gene encodes a precursor composed of a signal peptide, an N-terminal propeptide consisting of a core domain (N*) and a linker peptide, a subtilisin-like catalytic domain, a polycystic kidney disease domain (PkdD), and a chitin-binding domain (ChBD). Here we report that the autocatalytic maturation of SptC is initiated by cis-processing of N* to yield an autoprocessed complex (N*-I(WT)), followed by trans-processing/degradation of the linker peptide, the ChBD, and N*. The resulting mature form (M(WT)) containing the catalytic domain and the PkdD showed optimum azocaseinolytic activity at 3 to 3.5 M NaCl, demonstrating salt-dependent stability. Deletion analysis revealed that the PkdD did not confer extra stability on the enzyme but did contribute to enzymatic activity. The ChBD exhibited salt-dependent chitin-binding capacity and mediated the binding of N*-I(WT) to chitin. ChBD-mediated chitin binding enhances SptC maturation by promoting activation of the autoprocessed complex. Our results also demonstrate that SptC is capable of removing proteins from shrimp shell powder (SSP) at high salt concentrations. Interestingly, N*-I(WT) released soluble peptides from SSP faster than did M(WT). Most likely, ChBD-mediated binding of the autoprocessed complex to chitin in SSP not only accelerates enzyme activation but also facilitates the deproteinization process by increasing the local protease concentration around the substrate. By virtue of these properties, SptC is highly attractive for use in preparation of chitin from chitin-containing biomass.
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Yaoxin
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Mengxin
authors.initials: M
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Du
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Li
authors.initials: L
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Moran
authors.initials: M
authors.lastname: Li
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China Hubei Provincial Cooperative Innovation Center of Industrial Fermentation, Wuhan, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, China Hubei Provincial Cooperative Innovation Center of Industrial Fermentation, Wuhan, China tangxf@whu.edu.cn.
authors.forename: Xiao-Feng
authors.initials: XF
authors.lastname: Tang
mesh_terms: D002364:Caseins / Q000378:metabolism; D002686:Chitin / Q000378:metabolism*; D004795:Enzyme Stability; D015971:Gene Expression Regulation, Enzymologic; D006216:Halobacteriaceae / Q000201:enzymology* / Q000378:metabolism*; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D057057:Serine Proteases / Q000235:genetics / Q000378:metabolism*; D012965:Sodium Chloride / Q000378:metabolism
chemical_list: D002364:Caseins; C026018:azocasein; D002686:Chitin; D012965:Sodium Chloride; D057057:Serine Proteases