The conformation of dolichol.

ABSTRACT

An understanding of the natural conformation of dolichol is important for the elucidation of the mechanism of protein glycosylation and dolichol's other as yet undisclosed biological functions. Since the molecular mechanics method has been shown to be well suited for the prediction of alcohol and alkene conformations, we have employed it to study the conformations of apparent least energy of dolichol-19 and smaller polymers of isoprene, namely, squalene, trans,trans-farnesol, and cis,cis-farnesol. Additionally, the small-angle X-ray scattering (SAXS) method was employed to determine the validity of the apparent least energy conformer of dolichol-19 derived by the molecular mechanics method. The results indicate that the solution conformation of dolichol-19 is comprised of a central coiled region flanked by two arms. The central coiled region has two and a half turns of dimensions 9.84 x 16.55 x 51.66 A3. The arms of dimensions 3.99 x 5.89 x 17.47 A3 and 4.49 x 9.23 x 11.14 A3 are approximately diametrically opposed. Measurement of the intrinsic viscosity of dolichol in both isopentyl alcohol and oleyl alcohol showed that the natural conformation of dolichol is capable of increasing solution fluidity (i.e., lowering solution viscosity). Thus, while examination of the conformation of dolichol in a membrane-mimetic solvent by SAXS is not possible, the quantitative measure of the effect of dolichol on solution viscosity (and thus solution fluidity) is possible. The results are consistent with dolichol acting as a membrane-fluidizing agent and provide the first quantitative measure of the effect of dolichol on solution fluidity of a membrane-mimetic solvent.