title: Structural basis for Ca(2+)-induced activation of human PAD4.
abstract: Peptidylarginine deiminase 4 (PAD4) is a Ca(2+)-dependent enzyme that catalyzes the conversion of protein arginine residues to citrulline. Its gene is a susceptibility locus for rheumatoid arthritis. Here we present the crystal structure of Ca(2+)-free wild-type PAD4, which shows that the polypeptide chain adopts an elongated fold in which the N-terminal domain forms two immunoglobulin-like subdomains, and the C-terminal domain forms an alpha/beta propeller structure. Five Ca(2+)-binding sites, none of which adopt an EF-hand motif, were identified in the structure of a Ca(2+)-bound inactive mutant with and without bound substrate. These structural data indicate that Ca(2+) binding induces conformational changes that generate the active site cleft. Our findings identify a novel mechanism for enzyme activation by Ca(2+) ions, and are important for understanding the mechanism of protein citrullination and for developing PAD-inhibiting drugs for the treatment of rheumatoid arthritis.
authors.affiliation: Graduate School of Integrated Science, Yokohama City University, 1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama 230-0045, Japan.
authors.forename: Kyouhei
authors.initials: K
authors.lastname: Arita
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Shimizu
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Nakashima
authors.forename: Michiyuki
authors.initials: M
authors.lastname: Yamada
authors.forename: Mamoru
authors.initials: M
authors.lastname: Sato
mesh_terms: D020816:Amino Acid Motifs; D001120:Arginine / Q000737:chemistry; D001665:Binding Sites; D002104:Cadmium / Q000737:chemistry; D002118:Calcium / Q000737:chemistry* / Q000378:metabolism; D002384:Catalysis; D002956:Citrulline / Q000737:chemistry; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D006801:Humans; D006867:Hydrolases / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D007477:Ions; D008956:Models, Chemical; D008958:Models, Molecular; D016296:Mutagenesis; D009154:Mutation; D020641:Polymorphism, Single Nucleotide; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; D013379:Substrate Specificity
chemical_list: D007477:Ions; D002104:Cadmium; D002956:Citrulline; D001120:Arginine; D006867:Hydrolases; C000629235:PADI4 protein, human; D000080002:Protein-Arginine Deiminase Type 4; D000076342:Protein-Arginine Deiminases; D002118:Calcium