FULL PAPER DOI: 10.1002/ejoc.200600897 NMR Investigation of the Bound Conformation of Natural and Synthetic Oligomannosides to Banana Lectin Caroline Clavel, [a] Angeles Canales, [b] Garima Gupta, [c] F. Javier Cañada, [b] Soledad Penadés,* [a] Avadhesha Surolia,* [c,d] and Jesús Jiménez-Barbero* [b] Keywords: Mannose oligosaccharides / NMR spectroscopy / Molecular dynamics / Banana lectin / Molecular recognition The conformational behaviour of three mannose-containing oligosaccharides, namely, the α13[α16] trisaccharide, a heptasaccharide with α12, α13 and α16 linkages and a tetrasaccharide consisting of α13 and α12 linkages, when bound to banana lectin (BanLec) has been evaluated by trNOE NMR methods and docking calculations. It was found Introduction The recognition of high-mannose-type oligosaccharides plays a key role in protein quality control, with several in- tracellular proteins, such as lectins, chaperones and glycan- processing enzymes, being involved in this process. [1,2] A number of proteins bind the high-mannose saccharides found on the surface of the HIV-associated envelope glyco- protein gp120, thus interfering with the viral life cycle, providing a putative manner of controlling a variety of in- fections, including HIV. [3] These proteins are thought to rec- ognise high-mannose-type glycans with subtly different structures, although the precise specificities are yet to be clarified. In order to gain a better understanding of these protein–carbohydrate recognition events and as a key step for controlling them, access to well-defined mannose-con- taining oligosaccharides by means of organic synthesis methods is of paramount importance. [4,5] In addition, the possibility for these oligosaccharides to be part of saccha- ride-containing clusters is also highly desirable. [6] Indeed, it has been demonstrated that synthetic oligomannose clusters could mimic some of these carbohydrate epitopes (also in- cluding those of the 2G12 antibody), providing antigenic- ity. [7] Recently, gold glyconanoparticles (GNPs) have been [a] Grupo de Carbohidratos, IIQ-CSIC, Américo Vespucio 49, 41092 Sevilla, Spain E-mail: penades@iiq.csic.es [b] CIB-CSIC, Ramiro de Maeztu 9, 28040 Madrid, Spain E-mail: jjbarbero@cib.csic.es [c] Indian Institute of Science, Bangalore 560012, India [d] National Institute of Immunology, New Delhi 110067, India E-mail: surolia@mbu.iisc.ernet.in Supporting information for this article is available on the WWW under http://www.eurjoc.org or from the author. Eur. J. Org. Chem. 2007, 1577–1585 © 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1577 that the molecular recognition event involves a conforma- tional selection process with only one of the conformations present in the free state of the sugar being recognised at the lectin binding site. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) designed and used as new multivalent tools that mimic gly- coconjugate presentation on the cell surface. As key advan- tages, GNPs are highly soluble under physiological condi- tions, stable against enzymatic degradation and, more im- portantly, they are essentially non-toxic. [8] Therefore, GNPs may be used as suitable tools for basic studies of carbo- hydrate interactions and for intervention related to key bio- logical processes. [9] The precise three-dimensional structure and dynamics of the saccharides have important implications in these re- cognition events and, thus, an understanding of these par- ticular aspects is crucial for controlling the recognition events. [10] Herein, as part of a project devoted to the synthe- sis, interaction studies and applications of gold glyconano- particles, [11] we present the study of the banana lectin bound geometries of three linear and branched oligoman- nosides containing 12, 13 and 16 linkages. These molecules have been prepared as components of mannose- containing GNPs as potential microbicides that could block HIV-1 gp120 binding to DC-SIGN. We have decided to use banana lectin (BanLec) as the model lectin. BanLec is a dimeric plant lectin from the jacalin-related lectin family. [12] It is widely recognized that plant lectins are excellent model systems for the study of protein–carbohydrate interactions because of their robustness and ready availability. [13] More- over, it has been speculated that lectins of the jacalin family are involved in interactions with the gp120 glycoprotein. [3] Results and Discussion The three oligosaccharides studied herein show struc- tural features also present in the Man 9 GlcNAc 2 oligosac- charide, although they may be considered as fragments or non-natural modifications thereof. Therefore, experimental