Skip to main content
eScholarship
Open Access Publications from the University of California

UCLA

UCLA Electronic Theses and Dissertations bannerUCLA

Membrane Protein Topology Acquisition and Folding Through the Transition State

Abstract

The folding mechanisms of helical membrane proteins remain largely uncharted. Here we examine two of the primary events during membrane protein folding: insertion/topology acquisition into the lipid bilayer and the assembly of alpha helices into their native state. Towards this goal we characterize the kinetics of bacteriorhodopsin folding and employ φ-value analysis to explore the folding transition state. We were able to obtain reliable φ-values for 16 mutants of bacteriorhodopsin well distributed throughout the protein. Every φ-value was less than 0.4, indicating the transition state is not uniquely structured. We suggest that the transition state is a loosely organized ensemble of conformations. Before the final folding of the alpha helices, the transmembrane segments must be properly aligned in the lipid bilayer. The topology of helical membrane proteins is generally defined during insertion of the transmembrane helices. It is now clear, however, that topology can remain malleable in some cases. We show that the entire EmrE protein can indeed invert topology after the full protein is translated and inserted. Wholesale topology flipping is remarkable given the physical constraints of the membrane and exposes new avenues to envision folding pathways, both productive and detrimental.

Main Content
For improved accessibility of PDF content, download the file to your device.
Current View