National Center for Macromolecular Imaging
Fatty Acid Synthase

Obesity, a major health factor, is a measure of the fat deposited with adipose in consequence to food intake, fatty acid and triglyceride synthesis and oxidation, and energy homeostasis. Excess food provides not only the energy needs of the body, but promotes the synthesis of fatty acids and triglycerides and storage of the latter in liver and adipose tissues. The de novo synthesis of fatty acids from acetyl-CoA and malonyl-CoA in the presence of the reducing substrate NADPH is catalyzed by the enzyme fatty acid synthase, FAS, (EC 2-3-185). In animal tissues, including that of humans, FAS is a homodimer of a multifunctional protein (Mr 272,000). Each subunit protein contains seven catalytic activities plus the acyl carrier protein (ACP).

We present the first three-dimensional reconstruction of human fatty acid synthase, obtained by electron cryomicroscopy and single particle image processing. The structure shows that the synthase is composed of two monomers, arranged in an anti-parallel orientation, consistent with biochemical data. The monomers are connected to each other, at their middle, by a bridge of density, a site proposed to be the combination of the interdomain regions of the two monomers. Each monomer subunit appears to be subdivided into three structural domains. With this first reconstruction of the synthase, we propose a location for the enzyme's two fatty acid synthesis sites.

Normal mode analysis of a previously determined 19Å structure of FAS suggested that this enzyme might assume different conformational states with several distinct hinge movements. We have used a simultaneous multiple-model refinement method to search for the presence of the structural conformers from the electron images of FAS. We have demonstrated that the resulting models observed in the electron images are consistent with the predicted conformational changes. This technique demonstrates the potential of the combination of normal mode analysis with multiple model refinement to elucidate the multiple conformations of flexible proteins. Since each of these structures is based on a more homogeneous particle set, this technique has the potential, provided that sufficient references are used, to improve the resolution of the final reconstructions of single particles from electron cryomicroscopy.

Selected Publications

 
  • Brink, J., Ludtke, S. J., Yang, C. Y., Gu, Z. W., Wakil, S. J. and Chiu, W. (2002). Quaternary structure of human fatty acid synthase by electron cryomicroscopy. Proc. Natl. Acad. Sci. U S A 99: 138-143

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  • Ming, D., Kong, Y., Wakil, S.J., Brink, J., and Ma, J. (2002). Domain movements in human fatty acid synthase by quantized elastic deformational model. Proc Natl Acad Sci U S A 99, 7895-7899.

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  • Brink, J., Ludtke, S.J., Kong, Y., Wakil, S., Ma, J. and Chiu, W. (2004). Experimental verification of conformational variation of human fatty acid synthase as predicted by normal mode analysis. Structure, in press.

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