title: The crystal structure of a multidomain protease inhibitor (HAI-1) reveals the mechanism of its auto-inhibition.
abstract: Hepatocyte growth factor activator inhibitor 1 (HAI-1) is a membrane-bound multidomain protein essential to the integrity of the basement membrane during placental development and is also important in maintaining postnatal homeostasis in many tissues. HAI-1 is a Kunitz-type serine protease inhibitor, and soluble fragments of HAI-1 with variable lengths have been identifiedin vivoThe full-length extracellular portion of HAI-1 (sHAI-1) shows weaker inhibitory activity toward target proteases than the smaller fragments, suggesting auto-inhibition of HAI-1. However, this possible regulatory mechanism has not yet been evaluated. Here, we solved the crystal structure of sHAI-1 and determined the solution structure by small-angle X-ray scattering. These structural analyses revealed that, despite the presence of long linkers, sHAI-1 exists in a compact conformation in which sHAI-1 active sites in Kunitz domain 1 are sterically blocked by neighboring structural elements. We also found that in the presence of target proteases, sHAI-1 adopts an extended conformation that disables the auto-inhibition effect. Our results also reveal the roles of non-inhibitory domains of this multidomain protein and explain the low activity of the full-length protein. The structural insights gained here improve our understanding of the regulation of HAI-1 inhibitory activities and point to new approaches for better controlling these activities.
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Min
authors.initials: M
authors.lastname: Liu
authors.affiliation: College of Bioscience and Biotechnology, Fuzhou University, Fuzhou, Fujian, 350108, China. Electronic address: cyuan@fzu.edu.cn.
authors.forename: Cai
authors.initials: C
authors.lastname: Yuan
authors.affiliation: Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
authors.forename: Jan K
authors.initials: JK
authors.lastname: Jensen
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China.
authors.forename: Baoyu
authors.initials: B
authors.lastname: Zhao
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China; University of Chinese Academy of Sciences, Beijing 100049, China.
authors.forename: Yunbin
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China; College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China.
authors.forename: Longguang
authors.initials: L
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian, 350002, China; College of Chemistry, Fuzhou University, Fuzhou, Fujian 350108, China. Electronic address: mhuang@fjirsm.ac.cn.
authors.forename: Mingdong
authors.initials: M
authors.lastname: Huang
mesh_terms: D018360:Crystallography, X-Ray; D006801:Humans; D000072417:Protein Domains; D053491:Proteinase Inhibitory Proteins, Secretory / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
chemical_list: D053491:Proteinase Inhibitory Proteins, Secretory; C109149:SPINT1 protein, human
keywords: conformational change; crystal structure; protein crystallization; protein dynamic; protein structure; small-angle X-ray scattering (SAXS)