Correlation of 2J couplings with protein secondary structure

Geminal two‐bond couplings (²J) 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 ²J_CαN′, ²J_C′HN, ²J_HNCα, ²J_C′Cα, ²J_HαC′, ²J_HαCα, ²J_CβC′, ²J_N′Hα, ²J_N′Cβ, and ²J_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 ²J coupling constants studied to be retrieved. Grouped by their mediating nucleus, C′, N′ or C^α, ²J couplings related to C′ and N′ depend significantly on ?,ψ torsion‐angle combinations. β turn types I, I′, II and II′, especially, can be distinguished on the basis of relative‐value patterns of ²J_CαN′, ²J_HNCα, ²J_C′HN, and ²J_HαC′. These coupling types also depend on planar or tetrahedral bond angles, whereas such dependences seem insignificant for other types. ²J_HαCβ appears to depend on amino‐acid type only, showing negligible correlation with torsion‐angle geometry. Owing to its unusual properties, ²J_CαN′ can be considered a “one‐bond” rather than two‐bond interaction, the allylic analog of ¹J_N′Cα, as it were. Of all protein J coupling types, ²J_CαN′ exhibits the strongest dependence on molecular conformation, and among the ²J types, ²J_HNCα comes second in terms of significance, yet was hitherto barely attended to in protein structure work. Proteins 2010. © 2009 Wiley‐Liss, Inc.