Primary Citation of Related Structures: 1G7A, 1G7B
PubMed Abstract:
The structure of T(3)R(3) hexameric human insulin has been determined at 100 K from two different crystals at 1.2 and 1.3 A resolution and refined to residuals of 0.169 and 0.176, respectively. Owing to a phase change, the c axis is double its room-temperature value and the asymmetric unit contains two independent TR(f) insulin dimers ...
The structure of T(3)R(3) hexameric human insulin has been determined at 100 K from two different crystals at 1.2 and 1.3 A resolution and refined to residuals of 0.169 and 0.176, respectively. Owing to a phase change, the c axis is double its room-temperature value and the asymmetric unit contains two independent TR(f) insulin dimers. Compared with the orientation in the room-temperature structure, one dimer undergoes a rotation about the c axis of -5 degrees, while the second is rotated +4 degrees. A superposition of the backbone atoms of the two independent dimers shows that the C(alpha) atoms of five residues within the R(f)-state monomers are displaced by more than 1.0 A; smaller displacements are observed for the T-state monomers. Four zinc ions lie on the crystallographic threefold axis and each forms bonds to three symmetry-related HisB10 N(varepsilon2) atoms from the T- and R(f)-state trimers. While three of the zinc ions are tetrahedrally coordinated with a chloride ion completing the coordination sphere, mixed tetrahedral/octahedral coordination is observed for one of the T-state zinc ions. The three symmetry-related "phenolic binding sites" in one hexamer contain water molecules and a glycerol molecule, but the same sites in the second hexamer are occupied by a zinc ion coordinated to an alternate conformation of HisB10, a symmetry-related HisB5 and two chloride ions. Two additional and partially occupied zinc ion sites are observed at the interface between the two independent dimers. One zinc ion is coordinated by a T-state HisB5 of one dimer, an R-state HisB5 of the second dimer and two water molecules; the second zinc ion is coordinated by an alternate side-chain conformation of the T-state HisB5 and three water molecules. The carboxyl group of one GluB13 side chain, which exists in two discrete conformations, appears to be protonated, because short contacts exist to a second carboxyl group or to a carbonyl O atom.
Related Citations:
X-ray Crystallographic Studies on Hexameric Insulins in the Presence of Helix-Stabilizing Agents, Thiocyanate, Methylparaben, and Phenol Whittingham, J.L., Chaudhuri, S., Dodson, E.J., Moody, P.C.E., Dodson, G.G. (1995) Biochemistry 34: 15553
Crystallographic Evidence for Dual Coordination around Zinc in the T3R3 Human Insulin Hexamer Ciszak, E., Smith, G.D. (1994) Biochemistry 33: 1512
Structural stability in the 4-zinc human insulin hexamer Smith, G.D., Swenson, D.C., Dodson, E.J., Dodson, G.G., Reynolds, C.D. (1984) Proc Natl Acad Sci U S A 81: 7093
Structure of 4-zinc insulin Bentley, G., Dodson, E., Dodson, G.G., Hodgkin, D., Mercola, D. (1976) Nature 261: 166
The First Protein Crystal Structure Determined from High Resolution X-Ray Powder Diffraction Data: A Variant of T3R3 Human Insulin Zinc Complex Produced by Grinding Von Dreele, R.B., Stephens, P.W., Smith, G.D., Blessing, R.H. (2000) Acta Crystallogr D Biol Crystallogr 56: 1549
Organizational Affiliation:
Hauptman-Woodward Medical Research Institute, 73 High Street, Buffalo, NY 14203, USA. smith@hwi.buffalo.edu
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