[gmx-users] Calculation of twist angle in gmx helix

[Sridip Parui]

Dear Experts,

When "gmx helix" is run, we obatin severals outputs, one of them helix
"twist angle". I do not know how the paramter is being calculated. I
manually calculated the angle between succesive C-Alpha atoms, between
succesive backbone carbonyl C atoms and also between successive backbone N
atoms. But none of them is matching with the "gmc helix" generated values.
I want to take "number of residues per turn" as an order paramter. For
that, I need to calculate twist angle.

How exactly "twist angle" is calculated in "gmx helix"?
References with clear elaboration will be appreciated.

With regards,

Sridip Parui
Senior research fellow
Indian Association for the Cultivation of Science
Kolkata-700032, India