Orientational order and dynamics of hydration water in a single crystal ofbovine pancreatic trypsin inhibitor

Citation
K. Venu et al., Orientational order and dynamics of hydration water in a single crystal ofbovine pancreatic trypsin inhibitor, BIOPHYS J, 77(2), 1999, pp. 1074-1085
Citations number
46
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOPHYSICAL JOURNAL
ISSN journal
00063495 → ACNP
Volume
77
Issue
2
Year of publication
1999
Pages
1074 - 1085
Database
ISI
SICI code
0006-3495(199908)77:2<1074:OOADOH>2.0.ZU;2-D
Abstract
The orientational order and dynamics of the water molecules in form II crys tals of bovine pancreatic trypsin inhibitor (BPTI) are studied by H-2 NMR i n the temperature range 6-50 degrees C. From the orientation dependence of the single crystal quadrupole splitting and linewidth, the principal compon ents of the motionally averaged quadrupole interaction tensor and the irred ucible linewidth components for the orthorhombic crystal are determined. Wi th the aid of water orientations derived from neutron and x-ray diffraction , it is shown that the NMR data can be accounted for by a small number of h ighly ordered crystal waters, some of which have residence times in the mic rosecond range. Most of these specific hydration sites must be located at i ntermolecular contacts. The surface hydration layer that is also present in dilute solution is likely to be only weakly ordered and would then not con tribute significantly to the splining and linewidth from the protein crysta l. To probe water dynamics on shorter time scales, the 2H longitudinal rela xation dispersion is measured for a polycrystalline BPTI sample. The observ ed dispersion is dominated by rapidly exchanging deuterons in protein side chains, undergoing restricted rotational motions on a time scale of 10 ns.