title: Biochemical and structural analysis of Helix pomatia agglutinin. A hexameric lectin with a novel fold.
abstract: Helix pomatia agglutinin (HPA) is a N-acetylgalactosamine (GalNAc) binding lectin found in the albumen gland of the roman snail. As a constituent of perivitelline fluid, HPA protects fertilized eggs from bacteria and is part of the innate immunity system of the snail. The peptide sequence deduced from gene cloning demonstrates that HPA belongs to a family of carbohydrate-binding proteins recently identified in several invertebrates. This domain is also present in discoidin from the slime mold Dictyostelium discoideum. Investigation of the lectin specificity was performed with the use of glycan arrays, demonstrating that several GalNAc-containing oligosaccharides are bound and rationalizing the use of this lectin as a cancer marker. Titration microcalorimetry performed on the interaction between HPA and GalNAc indicates an affinity in the 10(-4) M range with an enthalpy-driven binding mechanism. The crystal structure of HPA demonstrates the occurrence of a new beta-sandwich lectin fold. The hexameric quaternary state was never observed previously for a lectin. The high resolution structure complex of HPA with GalNAc characterizes a new carbohydrate binding site and rationalizes the observed preference for alphaGalNAc-containing oligosaccharides.
authors.affiliation: Centre de Recherches sur les Macromolécules Végétales, CNRS, Université Joseph Fourier, 38041 Grenoble, France.
authors.forename: Jean-Frederic
authors.initials: JF
authors.lastname: Sanchez
authors.forename: Julien
authors.initials: J
authors.lastname: Lescar
authors.forename: Valérie
authors.initials: V
authors.lastname: Chazalet
authors.forename: Aymeric
authors.initials: A
authors.lastname: Audfray
authors.forename: Jean
authors.initials: J
authors.lastname: Gagnon
authors.forename: Richard
authors.initials: R
authors.lastname: Alvarez
authors.forename: Christelle
authors.initials: C
authors.lastname: Breton
authors.forename: Anne
authors.initials: A
authors.lastname: Imberty
authors.forename: Edward P
authors.initials: EP
authors.lastname: Mitchell
mesh_terms: D000116:Acetylgalactosamine; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002151:Calorimetry; D002240:Carbohydrate Sequence; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D018076:DNA, Complementary; D006372:Helix, Snails; D006388:Hemagglutinins; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D018076:DNA, Complementary; C038095:Helix lectin; D006388:Hemagglutinins; D037102:Lectins; D000116:Acetylgalactosamine