Structures of orthorhombic lysozyme grown at basic pH and its low-humidityvariant

The structures of orthorhombic lysozyme grown at basic pH and its low-humid ity variant have been solved and refined at 1.9 and 2.0 Angstrom resolution , respectively. A comparison of the native structure with those of crystals grown at acidic pH does not show any systematic pH-dependent difference in the molecular geometry. The conformations, mutual orientation and interact ions of the catalytic residues Glu35 and Asp52 also remain unchanged. Howev er, comparison between the native and low-humidity forms in the orthorhombi c form show that the changes in molecular geometry which accompany the wate r-mediated transformation to the low-humidity form are more pronounced in t he C-terminal residues than in the other regions of the molecule. During th e transformation from the native to the low-humidity form, the locations of only about half the water molecules in the hydration shell remain unchange d, but the hydration shell as a whole moves along with the protein molecule .