Conformational transitions of membrane-spanning peptides

跨膜肽的构象转变

Conformational transitions of membrane-spanning peptides Embedded in the membranes of all living cells, membrane proteins are the molecular links between the inside and outside world. These proteins, which represent 20-30% of all human genes, and 70% of drug targets approved by the FDA in the past decade, regulate molecular traffic and information flow across biological lipid bilayers. Given that critical mutations in membrane proteins underlie the causes of many human diseases, efforts to understand and control their structures are of great interest in basic and applied research. Mutations in membrane proteins can be regarded as biophysical events that influence not only packing and electrostatic interactions of membrane-spanning helices critical for function, but as well the compatibility of a given protein segment with the lipid bilayer environment of the cell. Our research thus focuses on the protein segments that constitute the basic components of membrane proteins. Under NSERC-funded research, for which the present application is a renewal, we have advanced the use of molecular design, chemical synthesis, and biochemical and biophysical approaches to unravel the ‘code’ as to how a given sequence is selected by a cell for membrane insertion, how the receiving lipid environment acts to stabilize the inserted segments, and ultimately how a change in a single amino acid can drastically alter a protein's biological fate. Building on this foundation, we propose to design and chemically synthesize several series of compositionally identical peptides to produce sequences of identical composition, but with varying placement and balance of hydrophobic and polar residues. We will assess peptide-lipid interactions by biochemical techniques such as gel electrophoresis and circular dichroism spectroscopy. In parallel, we will collaborate with Prof. Gunnar von Heijne (Stockholm University) - a world expert in membrane protein structure - to use a biological assay to determine the insertion propensity of the corresponding peptide sequences in vivo. We will then apply our findings to assess similar systematic sequence variations in the native transmembrane sequence of a single-spanning membrane protein. This research will define key principles about structure-function relationships in membrane protein folding and function. Our overall results will provide a wealth of fundamental information as to the nature of peptide- and protein interactions in membrane environments.