The binding mode of the complex is roughly determined during it0

The binding mode of the complex is roughly determined during it0 and then a pre-defined percentage of the top-ranking solutions according Thiazovivin to the HADDOCK-score (a weighted sum of electrostatics, van der Waals, restraint energies, buried surface area and an empirical desolvation term), are selected for further refinement. The consecutive refinement steps allow for small- to medium-range conformational changes while improving the overall score

of the models. The final structures are clustered based on their pairwise ligand interface RMSD (the root-mean-square-deviation of the atomic coordinates, considering only heavy backbone atoms, of interface residues belonging to the ‘ligand’ subunit(s) when all models are superimposed on the interface residues of the first subunit) and the average cluster scores are calculated over the top 4 members of each cluster. HADDOCK

was originally developed to make use of NMR data, and in particular of chemical shift perturbation data. Currently, it can translate most of the information sources listed in Table 1 and Table 2 into structural restraints GSK2118436 purchase (or additional scoring terms in the case of SAXS and CCS data [70]), except for cryo-EM data, although work in this direction is ongoing. All of these features are also offered via HADDOCK’s user-friendly web server interface [71] at We divide our discussion of applications of modeling large assemblies in two categories, based on the molecular topology, in symmetrical and non-symmetrical complexes. Many supramolecular assemblies exist as symmetrical oligomers. The symmetry in these systems combined with knowledge of the subunit structures can be used to guide the modeling of these assemblies. An inspiring application has come from Loquet et al. who focused on the needle of the Type III secretion system, an insoluble symmetric homomeric complex consisting of 80-residue monomers, resistant to crystallization [72]. Using ssNMR experiments on recombinant, selectively isotope labeled Type III needle, they were able to define unambiguous intra- and intersubunit distance restraints (Fig. 3). Needles

assembled from differentially labeled monomers were used to unambiguously identify inter-subunit contacts. EM measurements showed that the needle PDK4 is formed as a helix with ∼11 subunits per two turns. Starting from helically arrayed set of 29 monomers with an extended backbone conformation, they applied the fold-and-dock protocol of Rosetta [73], using the ssNMR chemical shifts, together with intra- and inter subunit distance restraints and the EM-based radius of the needle. In contrast to previous suggestions, the resulting structure revealed that N-terminal part of the subunit is located on the outside of the needle and mediates important inter-subunit interactions. Modeling symmetric oligomers when the oligomeric state is variable is extra challenging.

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