The Structure of Human Apolipoprotein A-IV as Revealed by Stable Isotope Assisted Cross-linking, Molecular Dynamics and Small Angle X-ray Scattering [Lipids]

January 14th, 2014 by Walker, R. G., Deng, X., Melchior, J. T., Morris, J., Tso, P., Jones, M. K., Segrest, J. P., Thompson, T. B., Davidson, W. S.

Apolipoprotein (apo)AIV plays important roles in dietary lipid and glucose metabolism and knowledge of its structure is required to fully understand the molecular basis of these functions. However, typical of the entire class of exchangeable apolipoproteins, its dynamic nature and affinity for lipid has posed challenges to traditional high-resolution structural approaches. We previously reported an X-ray crystal structure of a dimeric truncation mutant of apoAIV which showed a unique helix-swapping molecular interface. Unfortunately, the structures of the N and C termini that are important for lipid binding were not visualized. To build a more complete model, we used chemical cross-linking to derive distance constraints across the full length protein. The approach was enhanced with stable isotope labeling to overcome ambiguities in determining molecular span of the cross-links given the remarkable similarities in the monomeric and dimeric apoAIV structures. Using 51 distance constraints, we created a starting model for full-length monomeric apoAIV and then subjected it to two modeling approaches: i) molecular dynamics simulations and ii) fitting to small angle X ray scattering (SAXS) data. This resulted in the most detailed models yet for lipid free monomeric or dimeric apoAIV. Importantly, these models were of sufficient detail to direct the experimental identification of new functional residues that participate in a clasp mechanism to modulate apoAIV lipid affinity. The isotope assisted cross linking approach should prove useful for further study of this family of apolipoproteins in both the lipid free and bound states.
  • Posted in Journal of Biological Chemistry, Publications
  • Comments Off on The Structure of Human Apolipoprotein A-IV as Revealed by Stable Isotope Assisted Cross-linking, Molecular Dynamics and Small Angle X-ray Scattering [Lipids]