Simulation of Hydrated BPTI at High Pressure:  Changes in Hydrogen Bonding and Its Relation with NMR Experiments

This paper is focused on the structural changes occurring in hydrated bovine pancreatic trypsin inhibitor (BPTI) at varying hydrostatic pressure. We have carried out a series of nanosecond constant pressure simulations of BPTI at increasing pressure employing two popular force fields, AMBER and CHARMM. Results concerning the hydrogen bonds lengths and distribution underline differences in the two force fields. Overall, CHARMM predicts a compression of the BPTI backbone hydrogen bond network, while AMBER computes a slight increase in the length of these bonds. Compared to the experimental NMR estimate of hydrogen bond shortening, CHARMM, and to a minor extent AMBER, follow the experimental trend in the β -sheet and helix H2 regions of BPTI. Notwithstanding, both force fields show a rather large overall deviation from NMR findings.