Rapid internal dynamics of BPTI is insensitive to pressure N-15 spin relaxation at 2 kbar

Pressure effects on the backbone dynamics of a native basic pancreatic tryp sin inhibitor (BPTI) have been measured by N-15 spin relaxation and chemica l shifts at 30 and 2000 bar. The experiments utilized the on-line variable pressure cell nuclear magnetic resonance system on N-15-uniformly labeled B PTI at a proton frequency of 750.13 MHz at 36 degrees C. Longitudinal (R-1) and transverse (R-2) N-15 relaxation times and (H-1)-N-15 nuclear Overhaus er effects were measured for 41 protonated backbone nitrogens at both press ures. The model free analysis of the internal dynamics gave order parameter s for individual H-N vectors at both pressures. The results indicate that r apid internal dynamics in the ps-ns range for the polypeptide backbone is n ot significantly affected by pressure in the range between 30 bar and 2 kba r, The result is consistent with the linear pressure dependence of H-1 and N-15 chemical shifts of BPTI, which suggests that local compressibilities a nd amplitudes of associated conformational fluctuation are nearly invariant in the same pressure range. Overall, we conclude that at 2 kbar BPTI remai ns within the same native ensemble as at 1 bar, with a small shift of popul ation from that at 1 bar. (C) 2000 Federation of European Biochemical Socie ties.