Definition of Systematic, Approximately Separable, and Modular Internal Coordinates (SASMIC) for macromolecular...

Area of Science:

• Computational Chemistry
• Molecular Modeling
• Biophysics

Background:

• Accurate molecular modeling requires efficient internal coordinate systems.
• Existing Z-matrix methods have limitations in describing complex molecular movements.

Purpose of the Study:

• To introduce a novel set of internal coordinates, SASMIC, for systematic polypeptide analysis.
• To facilitate direct implementation in quantum chemistry packages and molecular dynamics simulations.
• To enable better separation of molecular vibrational modes.

Main Methods:

• Definition of a systematic numbering scheme for polypeptide groups and atoms.
• Development of Systematic, Approximately Separable, and Modular Internal Coordinates (SASMIC).
• Implementation of SASMIC in Z-matrix format with Perl scripts for automated generation.
• Application of SASMIC with ab initio quantum mechanical calculations.

Main Results:

• SASMIC coordinates allow for approximate separation of soft and hard molecular movements.
• Demonstrated application in assessing free energy approximations for side chain degrees of freedom.
• Hessian matrix analysis illustrates the separation of vibrational modes.

Conclusions:

• SASMIC provides a powerful and flexible coordinate system for molecular simulations.
• This approach enhances the efficiency and accuracy of computational studies on polypeptides.
• The method offers direct implementation of constraints and improved analysis of molecular dynamics.