Conformational Ensembles from Experimental Data and Computer Simulations

Conformational Ensembles from Experimental Data and Computer Simulations

Poster Abstracts

112-POS Board 32 Experimental Characterization of "Metamorphic" Proteins Predicted from an Ensemble- Based Thermodynamic Description James Wrabl 1,2 , Jordan Hoffmann 1,3 , Mark Sowers 2,4 , Vincent Hilser 1,2 . 2 Johns Hopkins University, Baltimore, MD, USA, 1 Johns Hopkins University, Baltimore, MD, USA, 3 Harvard University, Boston, MA, USA, 4 University of Texas Medical Branch, Galveston, TX, USA. The emerging biological phenomenon of "metamorphic" proteins, single amino acid sequences that adopt two physiologically distinct structures and functions, challenges current prediction methods largely reliant on sequence similarity. To address this problem, we develop an innovative metric for sequence-structure compatibility, using energetic information derived from an experimentally validated ensemble-based description of protein thermodynamics. The simulated ensemble's unique information, i.e. the locations of high and low stability, enthalpy, and entropy regions within a protein, is reduced to an eight-symbol code that permits efficient scoring of any structure against any amino acid sequence. Ensemble-based information from both native and denatured states is incorporated, with separate calibration of Gaussian probability models for background scores in each state. High-identity sequences, previously demonstrated in vitro to adopt either Streptococcus protein G A or G B folds, were correctly recapitulated, demonstrating that this ensemble-based compatibility metric indeed reflected the energetic determinants of fold. To further test this model, ten arbitrarily chosen uncharacterized members of the high-identity sequence space were expressed and purified; nine were found to be consistent with their predicted folds as assessed by circular dichroism spectroscopy. Several additional designed proteins, each containing a single Glycine mutation, appear to enable a fold switch between the G A and G B conformational ensembles. Complete biophysical characterizations and structure determinations are underway to confirm these conclusions. Since this ensemble-based scoring framework is applicable to any desired fold, it may be practically useful for the future targeted design, or large-scale proteomic detection, of novel metamorphic proteins.

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