Conformational Ensembles from Experimental Data and Computer Simulations

Conformational Ensembles from Experimental Data

and Computer Simulations

Poster Abstracts

149

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

Johns Hopkins University, Baltimore, MD, USA,

Johns Hopkins University, Baltimore, MD,

USA,

Harvard University, Boston, MA, USA,

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

or G

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

and G

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.