Scientific Report 2006

Molecular Biology

Developing Reagents for Stabilization of Membrane Proteins

Q. Zhang, M.G. Finn,* X. Ma, R.S. Roy

* Department of Chemistry, Scripps Research

Integral membrane proteins are extremely unstable outside the hydrophobic membrane bilayer, a situation that makes their in vitro biophysical and structural characterization difficult. An artificial environment is therefore needed to stabilize the proteins in their native state. We focus on developing new membrane-simulating reagents for the stabilization of membrane proteins for structural and functional studies.

Detergents, structurally similar to cell lipids, self-assemble into micellar structures and are indispensable in dissolving integral membrane proteins into single particles to facilitate protein crystallization. We intend to incorporate more hydrophobicity in the interior of detergent micelles to improve their stability and consequently their ability to stabilize integral membrane proteins. This change is accomplished by appending branches along the alkyl chains of detergents and, most interestingly, by adding a short branch at the interface between the hydrophobic tail and the hydrophilic head. These branches may behave in 2 distinct ways like small amphiphile additives successfully used in crystallization of integral membrane proteins, thereby decreasing the micellar radius and extruding water from the hydrophobic core of the micelles.

We are also working on a unique class of molecules with facial amphiphilicity. The facial amphiphiles are structurally distinct from the classical detergents that have end polarity. Although not clear, the binding mode with integral membrane proteins by the facial amphiphiles should differ from that of classical detergents. A smaller protein–facial amphiphile complex may be formed because of the amphiphile’s small aggregation number, which is expected to be beneficial for obtaining well-ordered protein crystals. We have shown that our newly designed facial amphiphiles can maintain the full catalytic function of an ATP-binding cassette transporter protein.

The structural determination of integral membrane proteins with our synthesized amphiphiles is being investigated in collaboration with members of the Center for Innovative Membrane Protein Technologies of the Joint Center for Structural Genomics at Scripps Research.

Publications

Bosco, D.A., Fowler, D.M., Zhang, Q., Nieva, J., Powers, E.T., Wentworth, P., Jr., Lerner, R.A., Kelly, J.W. Elevated levels of oxidized cholesterol metabolites in Lewy body disease brains accelerate α-synuclein fibrillization [published correction appears in Nat. Chem. Biol. 2:346, 2006]. Nat. Chem. Biol. 2:249, 2006.