Interactions of phenol and m-cresol in the insulin hexamer, and their effect on the association properties of B28 Pro -> Asp insulin analogues

J L Whittingham, D J Edwards, A A Antson, J M Clarkson, C G Dodson

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Insulin's natural tendency to form dimers and hexamers is significantly reduced in a mutant insulin B28 Pro --> Asp, which has been designed as a monomeric, rapid-acting hormone for therapeutic purposes. This molecule can be induced to form zinc hexamers in the presence of small phenolic derivatives which are routinely used as antimicrobial agents in insulin preparations. Two structures of B28 Asp insulin have been determined from crystals grown in the presence of phenol and Nz-cresol. in these crystals, insulin exists as R-6 zinc hexamers containing a number of phenol or nz-cresol molecules associated with aromatic side chains at the dimer-dimer inter-faces. At the monomer-monomer interfaces, the B28 Pro --> Asp mutation leads to increased conformational flexibility in the B chain C termini, resulting in the loss of important intermolecular van der Waals contacts, thus explaining the monomeric character of B28 Asp insulin. The structure of a cross-linked derivative of B28 Asp insulin, containing an Ala-Lys dipeptide linker between residues B30 Ala and Al Gly, has also determined. This forms an R-6 zinc hexamer containing several m-cresol molecules. Of particular interest in this structure are two nz-cresol molecules whose binding disrupted the beta-strand in one of the dimers. This observation suggests that the cross-link introduces mechanical strain on the B chain C terminus, thereby weakening the monomer-monomer interactions.

Original languageEnglish
Pages (from-to)11516-11523
Number of pages8
Issue number33
Publication statusPublished - 18 Aug 1998



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