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Arch Biochem Biophys. 2010 Jan 15;493(2):169-74. doi: 10.1016/j.abb.2009.10.007. Epub 2009 Oct 20.

The conformation of end-groups is one determinant of carotenoid topology suitable for high fidelity molecular recognition: a study of beta- and epsilon-end-groups.

Author information

1
Florida International University, Department of Chemistry and Biochemistry, Miami, FL 33199, USA. landrumj@fiu.edu

Abstract

Conformation affects a carotenoid's ability to bind selectively to proteins. We calculated adiabatic energy profiles for rotating the ring end-groups around the C6C7 bond and for flexing of the ring with respect to the polyene chain. The choice of computational methods is important. A low, 4.2 kcal/mol barrier to rotation exists for a beta-ring. An 8.3 kcal/mol barrier exists for rotation of an epsilon-ring. Rotation of the epsilon-ring is sensitive to substitution at C3. In the absence of external forces neither beta- nor epsilon-rings are rotationally constrained. The nearly parallel alignment of the beta-ring to the C6C7 bond axis contrasts to the more perpendicular orientation of the epsilon-ring. Flexion of a beta-ring to the minimized epsilon-ring conformation requires approximately 23 kcal/mol; extension of the epsilon-ring to the minimized beta-ring conformation requires approximately 8 kcal/mol. Selectivity associated with beta- versus epsilon-rings is dominated by the inability of the beta-ring to flex to minimize protein/ring steric interactions and maximize van der Waal's attractions with the binding site.

PMID:
19850003
DOI:
10.1016/j.abb.2009.10.007
[Indexed for MEDLINE]

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