NOMAD-Ref

NOMAD-Ref performs normal mode analysis and elastic network-based structural refinement to model large-amplitude biomolecular motions and to refine structures against X-ray diffraction structure factors, Cryo-EM maps, and small-angle X-ray scattering envelopes.

Key Features:

• Normal Mode Analysis: Employs normal mode analysis (NMA) on all-atom representations to describe collective motions in biomolecules with up to 100,000 atoms while bypassing the computational demands of full molecular dynamics.
• Elastic Network Model: Uses an elastic network model to predict structural transitions, including open/closed states in DNA-dependent polymerases, by focusing on low-frequency normal modes that correlate with experimental data.
• Structural Refinement: Refines biomolecular structures against X-ray diffraction structure factors, Cryo-EM maps, and small-angle X-ray scattering-derived envelopes via medium- or low-resolution reciprocal-space refinement using conjugate-gradient minimization.
• Deformation and Docking: Generates stereochemically correct decoys with large-amplitude deformations, quantifies overlaps between alternative conformations, and optimizes docked receptor/ligand complexes by modeling flexibility through normal mode motions.
• Predictive Modeling: Predicts structural changes upon complex formation and refines non-bonded intermolecular energies along low-frequency normal modes, correcting small ligand positional errors and handling motions unrelated to docking.
• Application to Macromolecular Complexes: Models inherent flexibility in macromolecular complexes, explains structural transitions with few parameters, and reduces over-fitting risk through cross-validation tests.

Scientific Applications:

• Drug Design: Predicts open/closed transitions in DNA-dependent polymerases to inform design of inhibitors that target these conformational changes.
• Structural Biology: Refines structures and predicts conformational changes to aid understanding of macromolecular interactions and dynamics.
• Cryo-EM and X-ray Crystallography: Enhances interpretation of Cryo-EM maps and X-ray crystallography or small-angle X-ray scattering envelopes by fitting models into molecular envelopes to improve structural reconstructions.

Methodology:

NOMAD-Ref integrates normal mode analysis with deformation and reciprocal-space structural refinement, using low-frequency normal modes and conjugate-gradient minimization to optimize structures against X-ray diffraction structure factors, Cryo-EM maps, and small-angle X-ray scattering envelopes.