Erwin London, Ph.D. Professor Department of Biochemistry and Cell Biology Center for Structural Biology Centers for Molecular Medicine Stony Brook University Stony Brook, NY 11794-5215 Office telephone: 631-632-8564 Fax: 631-632-8575 E-mail: elondon@notes.cc.sunysb.edu
Research Description

Membrane Protein Structure: Determining the Rules for Membrane Protein Translocation and Folding.

Our group is studying membrane protein structure and function by combining spectroscopic methods, such as fluorescence, with chemical, biochemical, immunochemical and molecular biological approaches. We are interested in the determining membrane protein structure and the origin of specific lipid-protein and protein-protein interactions. At present, we are concentrating on protein toxins that penetrate and translocate across cell membranes, such as diphtheria toxin. Our aim is to understand the mechanism of membrane penetration and translocation by this toxin. This should have important implications for protein translocation in general, as well as the design of therapeutic agents and vaccines for bacterial infections. To analyze the structure of diphtheria toxin in membrane site-directed mutagenesis is used to introduce site-directed fluorescence labels. The location of the residues relative to the membrane is then determined using antibody binding or a fluorescence quenching technique (parallax analysis) developed in our lab (see below). In this method the difference in the amount of fluorescence quenching of the fluorescently-labeled residue by lipids carrying quenching groups at different positions (depths) is used to calculate the depth of the fluorescent group.

We are also using studying the relationship between amino acid sequence and structure using simple transmembrane helices. Such helices are the main structural element within membrane proteins. We have begun studying the effect of introducing hydrophilic residues into a hydrophobic sequence. The identity, number and position of these residues within the sequence are being varied. Their structure and location within the bilayer is analyzed using fluorescence, fluorescence quenching, circular dichroism and other spectroscopic techniques. This will allow us to derive basic rules for membrane protein folding.

The Structure and Function of Cholesterol-Rich Membrane Domains

Together with Dr. Deborah Brown in the Dept. Of Biochemistry and Cell Biology we have been studying the structure and function of lipid domains enriched in cholesterol and sphingolipid. These domains have been proposed to have a functional role in processes such as viral and toxin entry into cells, protein sorting among organelles, signal transduction, prion formation and amyloid formation. Our studies involve determining the basic principles that drive the formation of these domains and regulate their lipid and protein composition.

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