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Open Access Highly Accessed Research article

The Ramachandran plots of glycine and pre-proline

Bosco K Ho1* and Robert Brasseur2

Author Affiliations

1 Department of Pharmaceutical Chemistry, University of California San Francisco, 600 16th St, San Francisco, CA 94107, USA

2 Centre de Biophysique Moléculaire Numérique, 2 Passage des déportés, B-5030 Gembloux, Belgium

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BMC Structural Biology 2005, 5:14  doi:10.1186/1472-6807-5-14

Published: 16 August 2005

Abstract

Background

The Ramachandran plot is a fundamental tool in the analysis of protein structures. Of the 4 basic types of Ramachandran plots, the interactions that determine the generic and proline Ramachandran plots are well understood. The interactions of the glycine and pre-proline Ramachandran plots are not.

Results

In glycine, the ψ angle is typically clustered at ψ = 180° and ψ = 0°. We show that these clusters correspond to conformations where either the Ni+1 or O atom is sandwiched between the two Hα atoms of glycine. We show that the shape of the 5 distinct regions of density (the α, αL, βS, βP and βPR regions) can be reproduced with electrostatic dipole-dipole interactions. In pre-proline, we analyse the origin of the ζ region of the Ramachandran plot, a region unique to pre-proline. We show that it is stabilized by a COi-1···CδHδi+1 weak hydrogen bond. This is analogous to the COi-1···NHi+1 hydrogen bond that stabilizes the γ region in the generic Ramachandran plot.

Conclusion

We have identified the specific interactions that affect the backbone of glycine and pre-proline. Knowledge of these interactions will improve current force-fields, and help understand structural motifs containing these residues.