Biochemical and structural analysis of Helix pomatia agglutinin. A hexameric lectin with a novel fold.
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.
Sanchez
Jean-Frederic
JF
Centre de Recherches sur les Macromolécules Végétales, CNRS, Université Joseph Fourier, 38041 Grenoble, France.
Lescar
Julien
J
Chazalet
Valérie
V
Audfray
Aymeric
A
Gagnon
Jean
J
Alvarez
Richard
R
Breton
Christelle
C
Imberty
Anne
A
Mitchell
Edward P
EP
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
D018076:DNA, Complementary; C038095:Helix lectin; D006388:Hemagglutinins; D037102:Lectins; D000116:Acetylgalactosamine