Laser photo CIDNP technique as a versatile tool for structural analysis of inter- and intramolecular protein-carbohydrate interactions

Crystallographic data on proteins are generally considered as definitive information on the structure. However, the problem remains that the defined structure is only valid for the crystallized protein, since crystal packing might favor distinct molecular arrangements. Also dynamic movements will be frozen at a certain position, and the often non-physiologic conditions used to induce/promote crystal growth may lead to favoring structures different from the population under physiological conditions. Thus it is helpful to team up crystallography with other experimental approaches to monitor protein attributes in solution. For this purpose, we herein focus on a NMR-spectroscopical technique, i.e. the laser photochemically induced dynamic nuclear polarization (CIDNP) method. Its scope of application is to assess surface accessibilities of histidine (His), tyrosine (Tyr), and/ or tryptophan (Trp) residues in a protein. To illustrate the value of mis technique, we demonstrate by CIDNP spectra of plant/animal lectins recorded in the absence and in the presence of their ligands, how to gain pertinent information about structural properties of the binding pocket in combination with modeling data. Next, glycoproteins are analyzed successfully with this method in order to delineate characteristic differences in the CIDNP spectra when the structure of the glycan chain is deliberately altered. Therefore, it is possible to address two major questions in glycosciences with the CIDNP method: the structural impact of a) oligosaccharide ligands in lectin-oligosaccharide complexes and b) covalently linked glycan chains present in glycoproteins.