Biochemical and Structural Analysis of Helix pomatia Agglutinin
A HEXAMERIC LECTIN WITH A NOVEL FOLD*
- Jean-Frederic Sanchez‡,1,2,
- Julien Lescar‡§,1,
- Valérie Chazalet‡,
- Aymeric Audfray‡,
- Jean Gagnon¶,
- Richard Alvarez∥,
- Christelle Breton‡,
- Anne Imberty‡,3 and
- Edward P. Mitchell**,4
- ‡Centre de Recherches sur les Macromolécules Végétales, CNRS (affiliated with Université Joseph Fourier), 38041 Grenoble, France, §School of Biological Sciences, Nanyang Technological University, 637616 Singapore, ¶CNRS-FRE2685, Université Joseph Fourier, 38706 La Tronche, France, ∥Department of Biochemical/Molecular Biology, University of Oklahoma, Oklahoma City, Oklahoma 73104, and **European Synchrotron Radiation Facility, Experiments Division, 38043 Grenoble, France
- ↵3 To whom correspondence may be addressed: CERMAV-CNRS BP53, 38041 Grenoble Cedex 09, France. Fax: 33-476547203; E-mail: imberty{at}cermav.cnrs.fr. 4 To whom correspondence may be addressed: European Synchrotron Radiation Facility, Experiments Division, BP 220, F-38043, Grenoble Cedex, France. Fax: 33-476882542; E-mail: mitchell{at}esrf.fr.
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 β-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 αGalNAc-containing oligosaccharides.
- Received April 11, 2006.
- Revision received May 15, 2006.
- The American Society for Biochemistry and Molecular Biology, Inc.
