De novo design of transmembrane helix-helix interactions and measurement of stability in a biological membrane.
Membrane proteins regulate a large number of cellular functions, and have great potential as tools for manipulation of biological systems. Developing these tools requires a robust and quantitative understanding of membrane protein folding and interactions within the bilayer. With this in mind, we have designed a series of proteins to probe the net thermodynamic contribution of well-known sequence motifs to transmembrane helix-helix association in a biological membrane. The proteins were designed from first principles (de novo) using current knowledge about membrane insertion and stabilizing interaction motifs. A simple poly-Leu "scaffold" was decorated with individual helix interaction motifs (G-XXX-G, polar residues, heptad repeat) to create transmembrane helix-helix interactions of increasing strength. The GALLEX assay, an in vivo assay for measurement of transmembrane helix self-association, was combined with computational methods to characterize the relative strength and mode of interaction for each sequence. In addition, the apparent free energy contribution (ΔΔGapp) of each motif to transmembrane helix self-association was measured in a biological membrane, results that are the first of their kind for these de novo designed sequences, and suggest that the free energy barrier to overcoming weak association is quite small (<1.4 kcal mol(-1)) in a natural membrane. By quantifying and rationalizing the contribution of key motifs to transmembrane helix association, our work offers a route to direct the design of novel sequences for use in biotechnology or synthetic biology (e.g. molecular switches) and to predict the effects of sequence modification in known transmembrane domains (for control of cellular processes).
MOAC Doctoral Training Centre, University of Warwick, Coventry CV4 7AL, UK.
Anthony
A
Nash
Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL, UK.
Rebecca
R
Notman
Department of Chemistry, University of Warwick, Coventry CV4 7AL, UK. Electronic address: ann.dixon@warwick.ac.uk.
Ann M
AM
Dixon
D020816:Amino Acid Motifs; D003198:Computer Simulation; D017076:Computer-Aided Design; D004926:Escherichia coli / Q000737:chemistry / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism*; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D029968:Escherichia coli Proteins; D008565:Membrane Proteins
Dissociation constant; GALLEX; Gibbs free energy; Membrane protein; Rational protein design