Geometry dependent two-dimensional heteronuclear multiplet effects in paramagnetic proteins

We report experimental observation and numerical simulation of a two-dimens ional multiplet effect in the heteronuclear correlation spectrum of a param agnetic protein that depends on molecular geometry. This effect arises as a consequence of cross-correlated relaxation involving the Curie spin relaxa tion and internuclear dipolar relaxation mechanisms. It also manifests itse lf in resolution and sensitivity improvement in transverse relaxation optim ised spectroscopy (TROSY) kind of experiments. Characteristic multiplet pat terns in heteronuclear coupled two-dimensional NMR spectra encode direction al information for the heteronuclear bond with respect to the paramagnetic center. These patterns, which are simulated here using Redfield's relaxatio n theory, can be used to obtain a new type of geometry restriction for stru cture determination and refinement of paramagnetic macromolecular systems.