Journal of Molecular Biology
Volume 228, Issue 4, 20 December 1992, Pages 1163-1176
Journal home page for Journal of Molecular Biology

Article
Role of B13 Glu in insulin assembly: The hexamer structure of recombinant mutant (B13 Glu → Gln) insulin

Dedicated to Dietrich Brandenburg on the occasion of the 60th anniversary of his birthday.
https://doi.org/10.1016/0022-2836(92)90323-CGet rights and content

Abstract

The assembly of the insulin hexamer brings the six B13 glutamate side-chains at the centre into close proximity. Their mutual repulsion is unfavourable and zinc co-ordination to B10 histidine is necessary to stabilize the well known zinc-containing hexamers. Since B13 is always a carboxylic acid in all known sequences of hexamer forming insulins, it is likely to be important in the hormone's biology. The mutation of B13 Glu → Gln leads to a stable zinc-free hexamer with somewhat reduced potency. The structures of the zinc-free B13 Gln hexamer and the 2Zn B13 insulin hexamer have been determined by X-ray analysis and refined with 2.5 Å and 2.0 Å diffraction data, respectively.

Comparisons show that in 2Zn B13 Gln insulin, the hexamer structure (T6) is very like that of the native hormone. On the other hand, the zinc-free hexamer assumes a quaternary structure (T3/R3) seen in the native 4Zn insulin hexamer, and normally associated only with high chloride ion concentrations in the medium. The crystal structures show the B13 Gln side-chains only contact water in contrast to the B13 glutamate in 2Zn insulin. The solvation of the B13 Gln may be associated with this residue favouring helix at B1 to B8. The low potency of the B13 Gln insulin also suggests the residue influences the hormone's conformation.

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  • Cited by (0)

    This research has been supported by the Juvenile Diabetes Foundaton (New York), the Medical Research Council and the Science and Engineering Research Council of the U.K. and the Deutsche Forschungsgemeinschaft (Wo 152/8-6). The discussions with Professor Michael Dunn, Professor Dorothy Hodgkin, Professor Don Steiner and Professor Howard Tager have greatly helped in the progress of the research and preparation of the paper. Atomatic co-ordinates and structure factors have been deposited with the Protein Data Bank. Brookhaven National Laboratory (Bernstein et al., 1977), and are available in machine readable form from the Protein Data Bank, Brookhaven or one of the affiliated centres at Melbourne or Osaka.

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