Correlation of 2 J couplings with protein secondary structure

Geminal two‐bond couplings ( 2 J ) in proteins were analyzed in terms of correlation with protein secondary structure. NMR coupling constants measured and evaluated for a total six proteins comprise 3999 values of 2 J CαN′ , 2 J C′HN , 2 J HNCα , 2 J C′Cα , 2 J HαC′ , 2 J HαCα , 2 J CβC′ , 2 J N′Hα , 2 J N′Cβ , and 2 J N′C′ , encompassing an aggregate 969 amino‐acid residues. A seamless chain of pattern comparisons across the spectrum datasets recorded allowed the absolute signs of all 2 J coupling constants studied to be retrieved. Grouped by their mediating nucleus, C′, N′ or C α , 2 J couplings related to C′ and N′ depend significantly on ϕ,ψ torsion‐angle combinations. β turn types I, I′, II and II′, especially, can be distinguished on the basis of relative‐value patterns of 2 J CαN′ , 2 J HNCα , 2 J C′HN , and 2 J HαC′ . These coupling types also depend on planar or tetrahedral bond angles, whereas such dependences seem insignificant for other types. 2 J HαCβ appears to depend on amino‐acid type only, showing negligible correlation with torsion‐angle geometry. Owing to its unusual properties, 2 J CαN′ can be considered a “one‐bond” rather than two‐bond interaction, the allylic analog of 1 J N′Cα , as it were. Of all protein J coupling types, 2 J CαN′ exhibits the strongest dependence on molecular conformation, and among the 2 J types, 2 J HNCα comes second in terms of significance, yet was hitherto barely attended to in protein structure work. Proteins 2010. © 2009 Wiley‐Liss, Inc.