The use of dipolar couplings for determining the solution structure of rat apo‐S100B(ββ)

Abstract

The relative orientations of adjacent structural elements without many well‐defined NOE contacts between them are typically poorly defined in NMR structures. For apo‐S100B(ββ) and the structurally homologous protein calcyclin, the solution structures determined by conventional NMR exhibited considerable differences and made it impossible to draw unambiguous conclusions regarding the Ca 2+ ‐induced conformational change required for target protein binding. The structure of rat apo‐S100B(ββ) was recalculated using a large number of constraints derived from dipolar couplings that were measured in a dilute liquid crystalline phase. The dipolar couplings orient bond vectors relative to a single‐axis system, and thereby remove much of the uncertainty in NOE‐based structures. The structure of apo‐S100B(ββ) indicates a minimal change in the first, pseudo‐EF‐hand Ca 2+ binding site, but a large reorientation of helix 3 in the second, classical EF‐hand upon Ca 2+ binding.