title: A novel subtilase inhibitor in plants shows structural and functional similarities to protease propeptides.
abstract: The propeptides of subtilisin-like serine proteinases (subtilases, SBTs) serve dual functions as intramolecular chaperones that are required for enzyme folding and as inhibitors of the mature proteases. SBT propeptides are homologous to the I9 family of protease inhibitors that have only been described in fungi. Here we report the identification and characterization of subtilisin propeptide-like inhibitor 1 (SPI-1) fromArabidopsis thalianaSequence similarity and the shared β-α-β-β-α-β core structure identified SPI-1 as a member of the I9 inhibitor family and as the first independent I9 inhibitor in higher eukaryotes. SPI-1 was characterized as a high-affinity, tight-binding inhibitor ofArabidopsissubtilase SBT4.13 withKdandKivalues in the picomolar range. SPI-1 acted as a stable inhibitor of SBT4.13 over the physiologically relevant range of pH, and its inhibitory profile included many other SBTs from plants but not bovine chymotrypsin or bacterial subtilisin A. Upon binding to SBT4.13, the C-terminal extension of SPI-1 was proteolytically cleaved. The last four amino acids at the newly formed C terminus of SPI-1 matched both the cleavage specificity of SBT4.13 and the consensus sequence ofArabidopsisSBTs at the junction of the propeptide with the catalytic domain. The data suggest that the C terminus of SPI-1 acts as a competitive inhibitor of target proteases as it remains bound to the active site in a product-like manner. SPI-1 thus resembles SBT propeptides with respect to its mode of protease inhibition. However, in contrast to SBT propeptides, SPI-1 could not substitute as a folding assistant for SBT4.13.
authors.affiliation: From the Institute of Plant Physiology and Biotechnology, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Mathias
authors.initials: M
authors.lastname: Hohl
authors.affiliation: From the Institute of Plant Physiology and Biotechnology, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Annick
authors.initials: A
authors.lastname: Stintzi
authors.affiliation: From the Institute of Plant Physiology and Biotechnology, University of Hohenheim, D-70593 Stuttgart, Germany andreas.schaller@uni-hohenheim.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schaller
mesh_terms: D000818:Animals; D017360:Arabidopsis / Q000737:chemistry* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism; D002417:Cattle; D017433:Protein Structure, Secondary; D015842:Serine Proteinase Inhibitors / Q000737:chemistry* / Q000378:metabolism; D013381:Subtilisins / Q000037:antagonists & inhibitors* / Q000737:chemistry* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D015842:Serine Proteinase Inhibitors; D013381:Subtilisins; C119297:subtilase, plant
keywords: intramolecular chaperone; molecular chaperone; plant biochemistry; prodomain; protease inhibitor; protein processing; proteolysis; serine protease; subtilase; subtilisin