High-Resolution Crystals of Methionine Aminopeptidase fromPyrococcus furiosusObtained by Water-Mediated Transformation

The monoclinic crystal form of methionine aminopeptidase fromPyrococcus furiosus(MAP-Pfu) has been crystallized from four different conditions. Native crystals belong to space group P21with typical unit-cell dimensionsa= 53.4,b= 85.1,c= 72.7 Å, β = 107.7° and diffract to 2.9–4.5 Å resolution. However, there is a problem of nonisomorphism among the crystals. Water-mediated transformation to low-humidity form occurs by reduction of the relative humidity of crystal environment to 79%. The unit-cell dimensions of transformed crystals area= 51.9,b= 83.3,c= 70.3 Å, β = 105.9°, and the calculated solvent content is 3.9% less than in original crystals. Transformation to low-humidity form is accompanied by 1.7 times reduction of overall temperature factors, extension of diffraction resolution up to 1.75 Å, without change or reduction of crystal mosaicity, and improvement in stability to X-ray radiation. The water-mediated transformation also appears to relieve the problem of nonisomorphism among the original MAP-Pfu crystals.