Nuclear magnetic resonance identification of "half-turn" and 3(10)-helix secondary structure in rabbit liver metallothionein-2.

Analysis of 1H-1H nuclear Overhauser effects and amide proton-C alpha proton coupling constants in rabbit liver metallothionein-2 resulted in the identification of two segments of 3(10)-helix and numerous secondary structure elements of a novel type, which we call "half-turn". A half-turn can be generated starting from a type II tight turn by rotation of phi 3 from +90 degrees to -90 degrees. Its appearance in metallothionein appears to be a consequence of the constraints on the polypeptide conformation by the large number of metal binding sites.