Crystallographic titration of cubic insulin crystals: pH affects GluB13 switching and sulfate binding

Acta Crystallogr D Biol Crystallogr. 2003 Apr;59(Pt 4):670-6. doi: 10.1107/s0907444903002208. Epub 2003 Mar 25.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Crystallization
  • Glutamic Acid / chemistry
  • Hydrogen-Ion Concentration
  • Insulin / chemistry*
  • Models, Molecular
  • Protein Binding
  • Protein Conformation
  • Sulfates / chemistry
  • Sulfates / metabolism
  • Swine
  • X-Ray Diffraction / statistics & numerical data

Substances

  • Insulin
  • Sulfates
  • Glutamic Acid