title: Crystal versus solution structures of enzymes: NMR spectroscopy of a crystalline serine protease.
abstract: The hydrogen-bonding status of His57 in the catalytic triad (Asp-His-Ser) of serine protease has important mechanistic implications for this class of enzymes. Recent nitrogen-15 nuclear magnetic resonance (NMR) studies of alpha-lytic protease find His57 and Ser195 to be strongly hydrogen-bonded, a result that conflicts with the corresponding crystallographic studies, thereby suggesting that the crystal and solution structures may differ. This discrepancy is addressed and resolved in a nitrogen-15 NMR study of the enzyme in the crystalline state. The results show that the His-Ser and Asp-His interactions are identical in crystals and solutions, but that in crystals His57 titrates with a pKa of 7.9, nearly one pKa unit higher than in solution. This elevated pKa accounts for the absence of the His-Ser hydrogen bond in previous x-ray studies.
authors.affiliation: Francis Bitter National Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: S O
authors.initials: SO
authors.lastname: Smith
authors.forename: S
authors.initials: S
authors.lastname: Farr-Jones
authors.forename: R G
authors.initials: RG
authors.lastname: Griffin
authors.forename: W W
authors.initials: WW
authors.lastname: Bachovchin
mesh_terms: D003460:Crystallization; D006639:Histidine; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D012694:Serine; D012697:Serine Endopeptidases; D012996:Solutions; D014961:X-Ray Diffraction
chemical_list: D012996:Solutions; D012694:Serine; D006639:Histidine; D012697:Serine Endopeptidases