Co-crystallization of the yeast phosphorelay protein YPD1 with the SLN1 response-regulator domain and preliminary X-ray diffraction analysis.

The SLN1, YPD1 and SSK1 proteins function in a multi-step phosphorelay signal transduction pathway in yeast. YPD1, a histidine-containing phosphotransfer (HPt) protein, mediates the transfer of a phosphoryl group between the two response-regulator domains associated with SLN1 and SSK1, the R1 and R2 domains, respectively. Co-crystallization of the SLN1-R1 domain with YPD1 is reported here. Two different crystal forms were obtained by the hanging-drop vapor-diffusion method using 2.6 M ammonium sulfate as a precipitant. X-ray diffraction analysis indicates that crystal form I belongs to a trigonal space group P3(2)/P3(1), with unit-cell parameters a = b = 91.4, c = 201.1 A, while crystal form II belongs to an orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 51.6, b = 74.2, c = 98.7 A. Complete data sets to 2.1 and 2.3 A resolution have been collected from trigonal and orthorhombic crystals, respectively. Protein gel analysis indicates that in both crystal forms YPD1 and the SLN1-R1 domain are present in a 1:1 stoichiometry suggestive of a complex.