STUDIES ON LONG-ACTING INSULIN - CRYSTAL-STRUCTURE OF ARG-B31 HUMAN INSULIN AT 2.0-ANGSTROM RESOLUTION

The crystal structure of Arg-B31 human insulin (ABHI), a long-acting i nsulin derivative, has been determined at 2.0 angstrom resolution by u sing X-ray diffraction analysis. The final crystallographic R factor o f the structure model after the refinement is 0.189 with the bond leng th r. m. s deviation of 0.018 angstrom. The refined structure of ABHI showed that the conformation of B-chain C-terminal residues was more s table than that in the native molecule. A striking structural feature of ABHI was in additional ion pair formed between Arg-B31 of molecule I and Glu-B21 of molecule II in a dimer, and three ionic bonds between the neighbouring molecules thereby appeared on the surface of ABHI he xamer. These secondary bonds generated by the insertion of the residue Arg-B31 should make the rate of dissociation of ABHI hexamer slow dow n when it was injected into the body and the property of protraction s hould be produced by a 'depot effect'. This ought to be the main struc ture basis of the prolonged action of ABHI. The results observed here demonstrate that the main idea we used in search for long-acting insul in is reasonable and correct which goes like this: making some additio nal non-covalent bonds between insulin monomers so as to slow down the dissociation of insulin oligomers and gain the protraction from a 'de pot effect', which may be used as a principle in the further research. It also shows an impressive example that the experimental result repo rted here is in agreement with the theoretical prediction before the s tructural determination.