Ultra-high resolution X-ray diffraction from crystals of the kinetic mutant of human carbonic anhydrase II, His 64 Ala, and its complexes with proton acceptor/donors.

Crystals of human carbonic anhydrase II with a specific point mutation, His 64 to Ala, have been grown in a solution of ammonium sulfate in the presence of mercury chloride. The crystals appear in approximately two weeks and belong to the monoclinic space group P2(1), with unit cell parameters of a = 42.2 Angstrom, b = 41.4 Angstrom c = 71.9 Angstrom beta = 104.2 degrees and one carbonic anhydrase molecule in the asymmetric unit. The crystals diffract X-rays beyond 1.0 Angstrom resolution. These crystals, soaked with exogenous proton acceptor/donors, will be used in X-ray and neutron diffraction studies to map the fine water structure "proton wire" in the active site of carbonic anhydrase and to assign the intra- and intermolecular proton transfer pathway(s) from the zinc-bound water out to the bulk solvent.