Modelling missing hydrogens from X-ray crystallography

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Discussion Overview

The discussion revolves around the modeling of missing hydrogen atoms in protein structures derived from X-ray crystallography data. Participants explore the physics and methodologies employed by a computer program that adds these hydrogens, as well as the implications of such additions in molecular simulations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses curiosity about the physics behind a program that adds missing hydrogen atoms to protein structures, seeking resources for further understanding.
  • Another participant suggests that the program should provide documentation on its methods as a starting point for understanding.
  • A request for more information about the specific software being used is made, indicating that details could clarify the discussion.
  • A later reply describes that if the software is VMD or similar, it likely places hydrogens at equilibrium bond distances based on force fields like CHARMM, Amber, or OPLS, but notes that this may not be accurate for protons in reaction centers.
  • It is mentioned that for bulk proteins, molecular simulations often keep hydrogens rigid using methods like SHAKE, which may affect the accuracy of the hydrogen placement.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the accuracy or methodology of hydrogen addition, with multiple viewpoints on the implications of using different software and force fields remaining present.

Contextual Notes

Limitations include the lack of specific details about the software in question and the assumptions made regarding the accuracy of hydrogen placement in various contexts.

Who May Find This Useful

This discussion may be useful for researchers and students interested in protein modeling, computational biology, and the implications of hydrogen atom placement in molecular simulations.

estalniath
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I had recently stumbled upon a computer program that can automatically add missing hydrogen atoms to protein structures from files from the protein data bank. (due to the hydrogen atom having only 1 electron, hence making its electron density too low to be detected by X-ray crystallography methods) I am curious on the physics used by the program to calculate and detect and add the hydrogen atom to those long chained molecules and would be more than delighted if someone could recommend me a book or web resources or even describe the theories here so that I can at least have a clear direction on which field/area to read up on to fully understand what is going on. :)
 
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The computer program should provide reference to how the program does what is does. That would be the first place to look.
 
Info about what software you are actually using would help as well.
 
If the program you are using is VMD, or something like it, then it is simply putting a hydrogen at the equilibrium bond distance and with an angle based upon the force field (CHARM, Amber, OPLS, etc).

You obviously would not consider this to be accurate if you're talking about a proton involved in a reaction center, etc. but for the bulk protein (where most molecular simulations will wind up holding hydrogens rigid via SHAKE anyway) it is fine.
 

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