DERIVING ACCURATE INTERPROTON DISTANCES FROM ROESY SPECTRA WITH LIMITED KNOWLEDGE OF SCALAR COUPLING-CONSTANTS VIA THE CARNIVAL ALGORITHM -AN ITERATIVE COMPLETE-RELAXATION-MATRIX APPROACH

A method (termed CARNIVAL) for accurately determining distances from p roton homonuclear rotating-frame Overhauser effect spectroscopy (ROESY ) is described. The method entails an iterative calculation of the rel axation matrix using methodology introduced with the MARDIGRAS algorit hm for analysis of two-dimensional nuclear Overhauser effect spectra ( B. A. Borgias and T. L. James, J. Magn. Reson. 87, 475, 1990). The sit uation is complicated in the case of ROESY as spectral peak intensitie s are influenced by resonance offset and contributions from homonuclea r Hartmann-Hahn (HOHAHA) transfer if the nuclear spins are related by scalar coupling. The effects of spin-locking field strength on distanc e determinations and the ensuing distance errors incurred when HOHAHA corrections are made with limited knowledge of scalar (J) coupling inf ormation have been evaluated using simulated ROESY intensities with a model peptide structure. It has been demonstrated that accurate distan ces can be obtained with little or no explicit knowledge of the homonu clear coupling constants over a moderate range of spin-locking field s trengths. The CARNIVAL algorithm has been utilized to determine distan ces in a decapeptide using experimental ROESY data without measured co upling constants. (C) 1995 Academic Press, Inc.