Neutron Laue diffraction study of concanavalin A - The proton of Asp28

Neutron Laue data collection, which harnesses a broader wavelength band emitted from the neutron source, opens up the prospect of studying larger proteins and/or using smaller protein crystals than is possible with monochromatic neutron protein crystallography data collection methods. Concanavalin A, a 25 kDa dagger protein was used in this study, albeit with a rather large crystal of 1.2 x 1.8 x 2.2 mm. Data in a resolution range of 8-2.75 Angstrom were used to refine the protein structure, which included many H/D sites; the final R-factor for the protein model and 61 waters was 0.207 (R-free = 0.310) for 4909 unique reflections. In particular, for example, the proton on Asp28 of concanavalin A, located previously by our 0.94 Angstrom synchrotron X-ray study, was also found in this neutron study; thus the two methods confirm each other. The Asp28 proton was found not to exchange, under the deuteriation conditions used. Negative neutron density was also observed for the manganese binding site consistent with the negative neutron scattering factor for this element. Concanavalin A is one of the first proteins studied by the neutron Laue technique. The limited exchange of H for D almost certainly can be improved upon thus reducing the proton background in the diffracton pattern. This in turn would allow the weaker, high-resolution reflections, to be recorded.