title: The regulatory mechanism of the caspase 6 pro-domain revealed by crystal structure and biochemical assays.
abstract: Caspase 6 (CASP6) is a neuron degeneration-related protease and is widely considered to be a potential drug-design target against neurodegenerative diseases such as Huntington's disease and Alzheimer's disease. The N-terminal pro-peptide of CASP6, also referred to as the pro-domain, contains 23 residues and its functional role remains elusive. In this study, the crystal structure of a full-length CASP6 zymogen mutant, proCASP6H121A, was solved. Although the pro-domain was flexible in the crystal, without visible electron density, structural analyses combined with biochemical assays revealed that the pro-domain inhibited CASP6 auto-activation by inhibiting intramolecular cleavage at the intersubunit cleavage site TEVD(193) and also by preventing this site from intermolecular cleavage at low protein concentration through a so-called `suicide-protection' mechanism. Further experiments showed that the length of the pro-domain and the side chain of Asn18 played critical roles in suicide protection. These results disclosed a new inhibitory mechanism of CASP6 and shed light on the pathogenesis and therapeutically relevant study of CASP6-related neurodegenerative diseases.
authors.affiliation: State Key Laboratory of Protein and Plant Gene Research, and Biodynamic Optical Imaging Center (BIOPIC), School of Life Sciences, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Qin
authors.initials: Q
authors.lastname: Cao
authors.affiliation: State Key Laboratory of Protein and Plant Gene Research, and Biodynamic Optical Imaging Center (BIOPIC), School of Life Sciences, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Protein and Plant Gene Research, and Biodynamic Optical Imaging Center (BIOPIC), School of Life Sciences, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Lan-Fen
authors.initials: LF
authors.lastname: Li
authors.affiliation: State Key Laboratory of Protein and Plant Gene Research, and Biodynamic Optical Imaging Center (BIOPIC), School of Life Sciences, Peking University, Beijing 100871, People's Republic of China.
authors.forename: Xiao-Dong
authors.initials: XD
authors.lastname: Su
mesh_terms: D053178:Caspase 6 / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D006801:Humans; D008958:Models, Molecular; D009154:Mutation; D019636:Neurodegenerative Diseases / Q000201:enzymology; D017434:Protein Structure, Tertiary
chemical_list: D053178:Caspase 6
keywords: activation; caspase 6; full-length zymogen; neurodegenerative diseases; pro-domain