Constraints torsion angle

Similarly to distance constraints, torsion angle constraints have been implemented with various analytical expressions. Common to all implementations is that the potential should be zero for allowed values of the angle and positive otherwise. In addition, the potential and its derivative should be continuous. One possible expression is given below. 

The molecular structure of the amyloid fibrils formed by fragment 105-115 of transthyretin (TTR10sns, YTIAALLSPTS) has been characterized by solid-state NMR. The fibril backbone structure was first established based on the TALOS analysis of the 15N and 13C chemical shifts [89]. Using the correlation experiments of Hn(0-N(0—CV-H0 , Ha(0-Ca(0-N(i.+1)-HN(i+1), and N -Tco-N, a total of 41 constraints on 19 backbone torsion angles have been obtained in a... 

Torsion Angle Constraints from Chemical Shifts... 

Torsion Angle Constraints from Scalar Coupling Constants... 

The role of the potential energy is taken by the Dyana target function [8, 28] that is defined such that it is zero if and only if all experimental distance constraints and torsion angle constraints are fulfilled and all nonbonded atom pairs satisfy a check for the absence of steric overlap. A conformation that satisfies the constraints more closely than another one will lead to a lower target function value. The exact definition of the Dyana target function is ... 

Upper and lower bounds, bap, on distances da/3 between two atoms a and b, and constraints on individual torsion angles 0i in the form of allowed intervals [f 111, 13 ] are considered. Iu, h and Iv are the sets of atom pairs (a, /I) with upper, lower or van der Waals distance bounds, respectively, and Ia is the set of restrained torsion angles. wu, Wj, wv and wa are weighting factors for the different types of constraints. 

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