Ester carbonyl vibration as a sensitive probe of protein local electric field.

Ileana M Pazos, Ayanjeet Ghosh, Matthew J Tucker, Feng Gai

Index: Angew. Chem. Int. Ed. Engl. 53(24) , 6080-4, (2014)

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Abstract

The ability to quantify the local electrostatic environment of proteins and protein/peptide assemblies is key to gaining a microscopic understanding of many biological interactions and processes. Herein, we show that the ester carbonyl stretching vibration of two non-natural amino acids, L-aspartic acid 4-methyl ester and L-glutamic acid 5-methyl ester, is a convenient and sensitive probe in this regard, since its frequency correlates linearly with the local electrostatic field for both hydrogen-bonding and non-hydrogen-bonding environments. We expect that the resultant frequency-electric-field map will find use in various applications. Furthermore, we show that, when situated in a non-hydrogen-bonding environment, this probe can also be used to measure the local dielectric constant (ε). For example, its application to amyloid fibrils formed by Aβ(16-22) revealed that the interior of such β-sheet assemblies has an ε value of approximately 5.6.© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.