title: Structural and phylogenetic relationships among plant and animal cystatins.
abstract: The plant cystatins or phytocystatins (PhyCys) are cysteine proteinase inhibitors containing the QxVxG motif and have been placed in the cystatin superfamily of proteins. The primary sequences of PhyCys have a high degree of homology with the members of the cystatin family, but they resemble stefins by the absence of disulfide bonds and cysteine residues. A multialignment and a phylogenetic analysis of 63 cystatins, 32 of which are PhyCys, demonstrate that all PhyCys cluster in a major evolutionary tree branch and support the classification of PhyCys as a new cystatin family. The PhyCys also possess a specific consensus sequence [LVI]-[AGT]-[RKE]-[FY]-[AS]-[VI]-x-[EDQV]-[HYFQ] -N placed on the region corresponding to a predictable amino-terminal alpha-helix. This sequence can be used to specifically identify PhyCys on protein data banks and to differentiate them from the other members of the superfamily.
authors.affiliation: Department of Biochemistry, Federal University of Rio de Janeiro, Rio de Janeiro, RJ, 21949-900, Brazil. margisr@chagas.biof.ufrj.br
authors.forename: R
authors.initials: R
authors.lastname: Margis
authors.forename: E M
authors.initials: EM
authors.lastname: Reis
authors.forename: V
authors.initials: V
authors.lastname: Villeret
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D015891:Cystatins / Q000737:chemistry* / Q000235:genetics*; D003545:Cysteine / Q000737:chemistry; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010649:Phenylalanine / Q000737:chemistry; D010802:Phylogeny; D010944:Plants / Q000737:chemistry* / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D015891:Cystatins; D010649:Phenylalanine; D003545:Cysteine