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

Pressure effects on the backbone dynamics of a native basic pancreatic trypsin inhibitor (BPTI) have been measured by (15)N spin relaxation and chemical shifts at 30 and 2000 bar. The experiments utilized the on-line variable pressure cell nuclear magnetic resonance system on (15)N-uniformly labeled BPTI at a proton frequency of 750.13 MHz at 36 degrees C. Longitudinal (R(1)) and transverse (R(2)) (15)N relaxation times and ((1)H)-(15)N nuclear Overhauser effects were measured for 41 protonated backbone nitrogens at both pressures. The model free analysis of the internal dynamics gave order parameters for individual H-N vectors at both pressures. The results indicate that rapid internal dynamics in the ps-ns range for the polypeptide backbone is not significantly affected by pressure in the range between 30 bar and 2 kbar. The result is consistent with the linear pressure dependence of (1)H and (15)N chemical shifts of BPTI, which suggests that local compressibilities and amplitudes of associated conformational fluctuation are nearly invariant in the same pressure range. Overall, we conclude that at 2 kbar BPTI remains within the same native ensemble as at 1 bar, with a small shift of population from that at 1 bar.