NDLI: Extensive counter-ion interactions seen at the surface of subtilisin in an aqueous medium

Content Provider	Royal Society of Chemistry (RSC)
Author	Negroni, Jacopo Cianci, Michele Helliwell, John R. Halling, Peter J.
Copyright Year	2014
Abstract	The extent of protein and counter-ion interactions in solution is still far from being fully described and understood. In low dielectric media there is documented evidence that counter-ions do bind and affect enzymatic activity. However, published crystal structures of macromolecules of biological interest in aqueous solution often do not report the presence of any counter-ions on the surface. The extent of counter-ion interactions within subtilisin in an aqueous medium has been investigated crystallographically using CsCl soak and X-ray wavelength optimised anomalous diffraction at the Cs K-edge. Ten Cs+, as well as six Cl− sites, have been clearly identified, revealing that in aqueous salt solutions ions can bind at defined points around the protein surface. The counter-ions do not generally interact with formal charges on the protein; formally neutral oxygens, mostly backbone carbonyls, mostly coordinate the Cs+ ions. The Cl− ion sites are also found likely to be near positive charges on the protein surface. The presence of counter-ions substantially changes the protein surface electrical charge. The surface charge distribution on a protein is commonly discussed in relation to enzyme function. The correct identification of counter-ions associated with a protein surface is necessary for a proper understanding of an enzyme's function.
Starting Page	36771
Ending Page	36776
Page Count	6
File Format	HTM / HTML PDF
ISSN	20462069
Volume Number	4
Issue Number	69
Journal	RSC Advances
DOI	10.1039/c4ra06448h
Language	English
Publisher	Royal Society of Chemistry
Access Restriction	Open
Subject Keyword	X-ray crystallography Neutron diffraction Enzyme Interaction Ion Subtilisin K-edge Dielectric Protein Wavelength
Content Type	Text
Resource Type	Article
Subject	Chemistry Chemical Engineering

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