What is it about?
The power of X-ray crystal structure analysis as a technique is to ‘see where the atoms are’. The results are extensively used by a wide variety of research communities. However, this ‘seeing where the atoms are’ can give a false sense of security unless the precision of the placement of the atoms has been taken into account. Indeed, the presentation of bond distances and angles to a false precision (i.e. to too many decimal places) is commonplace.
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Why is it important?
The end point of protein structure model refinement requires a knowledge of the individual atomic position errors. A Salt Bridges in Protein Structures (SBPS) webtool (http://cluster.physics.iisc.ernet.in/dpi/) has been designed and created to help to understand the nature and geometry of the ion pairs found in protein structures. Also an online computing server to estimate the atomic coordinate errors for all the atoms in any protein structure is at the URL http://cluster.physics.iisc.ernet.in/dpi/. All this is important because until now the errors on each of the the atomic coordinates in biological structures have not not been individually displayed and a false precision often assumed including in widely used molecular graphics tools.
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This page is a summary of: Do we see what we should see? Describing non-covalent interactions in protein structures including precision, IUCrJ, December 2013, International Union of Crystallography,
DOI: 10.1107/s2052252513031485.
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Resources
A webtool to calculate the error on any protein PDB file atom.
An online computing server, Diffraction Precision Index (DPI), has been created and maintained to calculate the ‘Cruickshank DPI’ value for a given three-dimensional protein or macromolecular structure. Also, it estimates the atomic coordinate error for all the atoms available in the structure. D. W. J. Cruickshank (1999). Acta. Cryst. D 55, 583–601. M. Gurusaran, M. Shankar, R. Nagarajan, J. R. Helliwell & K. Sekar (2014). IUCrJ 1, 74-81. K. S. Dinesh Kumar et al J Appl Cryst in press.
A webtool lto calculate ion pair distances and their precisions
The SBPS webtool has been designed and created to help to understand the nature and geometry of the ion pairs found in protein structures. The atomic positional uncertainty has been taken into account to address the error in the ionic interaction distance associated with a given salt bridge. Thus, it can be employed to shed light on the role of ion pairs in protein stability, folding, behaviour and function. Furthermore, SBPS will contribute significantly to ion-pair-related mutational studies and drug-development research.
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