Conformation of the Drosophila motor protein non-claret disjunctional in solution from x-ray and neutron scattering

The quaternary structures of monomeric and dimeric Drosophila non-claret di sjunctional (ncd) constructs were investigated using synchrotron x-ray and neutron solution scattering, and their low resolution shapes were restored ab initio from the scattering data, The experimental curves were further co mpared with those computed from crystallographic models of one monomeric an d three available dimeric ncd structures in the microtubule-independent ADP -bound state, These comparisons indicate that accounting for the missing pa rts in the crystal structures for all these constructs is indispensable to obtain reasonable fits to the scattering patterns. A ncd construct (MC6) la cking the coiled-coil region is monomeric in solution, but the calculated s cattering from the crystallographic monomer yields a poor fit to the data. A tentative configuration of the missing C-terminal residues in the form of an antiparallel beta -sheet was found that significantly improves the fit. The atomic model of a short dimeric ncd construct (MC5) without 2-fold sym metry is found to fit the data better than the symmetric models, Addition o f the C-terminal residues to both head domains gives an excellent fit to th e x-ray and neutron experimental data, although the orientation of the beta -sheet differs from that of the monomer, The solution structure of the lon g ncd construct (MC1) including complete N-terminal coiled-coil and motor d omains is modeled by adding a straight coiled-coil section to the model of MC5.