CHIRAL RAMACHANDRAN PLOTS: GLYCINE

Ramachandran plots are classical analytical tools for the structural characterization of proteins. These plots are based on two types of torsion angles within the polypeptide backbone. Despite their wide use, these plots provide only limited information on the detailed structure of the analyzed proteins. We show that by extending the structural analysis to include the quantitative degree of chirality of the relevant amino-acid segments, much richer informative 3D maps are obtained. Specifically we focus here on glycine, and highlight the fact that contrary to its definition as the only achiral amino-acid, it is practically always conformationally chiral within the proteins. The degree of chirality is evaluated quantitatively by means of the Continuous Chirality Measure (CCM) metodology^1,2. A very large library of 10,376 glycine units extracted from crystallographic data of 161 proteins was analyzed, revealing structural trends that are hidden in the classical Ramachandran plots. This study shows that combining the original Ramachandran plot with the CCM analysis is a powerful new tool for the structural analysis of proteins. Extension to other amino-acids is in progress.

This research was supported by The Open University of Israel`s Research Fund, grant no. 504801, and the Israel Science Foundation (grant No. 411/15).

References:

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2. Alemany P., Casanova D. & Alvarez, S. (2012) Phys. Chem. Chem. Phys. 44, 11816-11823;