W0440

Neutrons, Protons and Proteins. D.A.A. Myles, EMBL - Grenoble Outstation, 6 rue Jules Horowitz, BP 181, 38042 Grenoble Cedex 9 France.

Neutron diffraction offers unique advantages for molecular structural biology by enabling key and individual hydrogen atoms to be located in biological structures that cannot be seen by X-ray analysis alone. In the past, the problems associated with the relatively low flux of available neutron beams have restricted such application to only a few projects of specific technical interest. The field of neutron protein crystallography is now undergoing significant development as new detector technologies and parallel advances in molecular biology push the capabilities towards atomic resolution. A new generation of advanced 2-D protein neutron diffractometers are being built worldwide. In Europe, for example, the LADI Laue diffractometer at ILL/EMBL provides dedicated facilities for neutron protein crystallography that allow high-resolution (1.5Å) data to be collected with 10-100 fold gains in efficiency compared with conventional neutron diffractometers. However, the large hydrogen incoherent scattering background in biological crystallography places severe limitations on sample size, data collection times and, ultimately, on the quality of the final analysis. This can be significantly improved by the use of fully (per)deuterated samples. Recent developments in deuterium-labelling technologies therefore promise additional gains that will extend capabilities towards the solution of more complex biological problems. These advances make feasible studies of larger biological complexes and smaller crystals than previously possible. We will review the significant developments in the field and present examples of their application to problems concerning enzymatic mechanism, ligand binding interactions, solvent effects, structure dynamics and their implications.