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. [ABSTRACT FROM AUTHOR]