Crystallographic titration of cubic insulin crystals: pH affects GluB13 switching and sulfate binding.
Structures of porcine insulin crystals soaked in 1 M sodium sulfate at pH 5.00, 5.53, 5.80, 6.00, 6.16, 6.26, 6.35, 6.50, 6.98 and 9.00 have been determined at between 1.7 and 1.9 A resolution. GluB13 exhibits a single conformation at pH </= 5.80, two conformations between pH 6.00 and 6.98 and a single conformation at pH 9.00. Between pH 6.00 and 6.98, the conformation of GluB13 switches from one rotamer to another rotamer. Between pH 6.16 and 6.26, PheB1 undergoes a significant conformational change. By pH 9.00 many residues have undergone relatively large shifts and HisB10 exhibits a double conformation. As a result of the pH increase, the occupancy of the sulfate ion decreases from a maximum of 1.00 at pH 5.00 to a minimum of 0.46 at pH 6.50. Comparison of the structures, the observed and calculated structure factors and map correlation coefficients indicate that the porcine insulin structure changes gradually as a function of pH.
Diao
Jiasheng
J
Institute of Molecular Biophysics, Florida State University, Tallahassee 32306, USA. diao@bilbo.bio.purdue.edu
D000818:Animals; D003460:Crystallization; D018698:Glutamic Acid / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000737:chemistry*; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism; D013552:Swine; D014961:X-Ray Diffraction / Q000706:statistics & numerical data
D007328:Insulin; D013431:Sulfates; D018698:Glutamic Acid