title: Crystal structure of cardosin A, a glycosylated and Arg-Gly-Asp-containing aspartic proteinase from the flowers of Cynara cardunculus L.
abstract: Aspartic proteinases (AP) have been widely studied within the living world, but so far no plant AP have been structurally characterized. The refined cardosin A crystallographic structure includes two molecules, built up by two glycosylated peptide chains (31 and 15 kDa each). The fold of cardosin A is typical within the AP family. The glycosyl content is described by 19 sugar rings attached to Asn-67 and Asn-257. They are localized on the molecular surface away from the conserved active site and show a new glycan of the plant complex type. A hydrogen bond between Gln-126 and Manbeta4 renders the monosaccharide oxygen O-2 sterically inaccessible to accept a xylosyl residue, therefore explaining the new type of the identified plant glycan. The Arg-Gly-Asp sequence, which has been shown to be involved in recognition of a putative cardosin A receptor, was found in a loop between two beta-strands on the molecular surface opposite the active site cleft. Based on the crystal structure, a possible mechanism whereby cardosin A might be orientated at the cell surface of the style to interact with its putative receptor from pollen is proposed. The biological implications of these findings are also discussed.
authors.affiliation: Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Apartado 127, 2780-Oeiras, Portugal.
authors.forename: C
authors.initials: C
authors.lastname: Frazão
authors.forename: I
authors.initials: I
authors.lastname: Bento
authors.forename: J
authors.initials: J
authors.lastname: Costa
authors.forename: C M
authors.initials: CM
authors.lastname: Soares
authors.forename: P
authors.initials: P
authors.lastname: Veríssimo
authors.forename: C
authors.initials: C
authors.lastname: Faro
authors.forename: E
authors.initials: E
authors.lastname: Pires
authors.forename: J
authors.initials: J
authors.lastname: Cooper
authors.forename: M A
authors.initials: MA
authors.lastname: Carrondo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001216:Asparagine; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry* / Q000302:isolation & purification; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006031:Glycosylation; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000737:chemistry* / Q000302:isolation & purification; D018547:Plant Stems / Q000201:enzymology; D010944:Plants / Q000201:enzymology*; D017433:Protein Structure, Secondary
chemical_list: D010940:Plant Proteins; D001216:Asparagine; D016282:Aspartic Acid Endopeptidases; C097455:aspartic proteinases, Cynara cardunculus