Structure and function of selected membrane proteins
Mechanisms of secretory vesicle fusion with membranes
4152 Molecular Biology Building
Dept. of Biochemistry, Biophysics & Molecular Biology
Iowa State University
Ames, IA 50011
Phone: (515) 294-2530
B.S., Seoul National University,1982
Ph.D., Cornell University, 1990
Postdoctoral Fellow, UCLA, 1990-1993
In Professor Shin’s laboratory a new spin labeling EPR approach is used to study the structure and function of biologically important membrane proteins. The strategy is to site-specifically place a nitroxide spin label in the protein by replacing a native residue with cysteine, which provides a unique labeling sites. Current developments of EPR technology make it possible to obtain information on secondary and tertiary structures as well as membrane topology using spin labeled mutants. Unlike crystallographic methods, the EPR approach does not require crystallization of proteins. Thus, the EPR methods are widely applicable to studies of many important membrane proteins. Furthermore, the mechanistic aspects of the function of the membrane proteins are studied using the time-resolved EPR techniques. Specific areas of current interest include:
The viral envelope proteins: influenza HA and HIV gp160
The influenza virus surface is coated with the HA protein which play a major role in the infection of host cells. The primary function of HA is to bring the viral and cellular membranes close together so that they can fuse. Fusion allows the virus genome into the host cell where it replicates. The protein conformational change and its interaction with the cellular membranes are, however, largely unknown. In our laboratory we express the membrane interacting domain of HA in E. coli. Spin labeling EPR and the crystallographic studies are pursued in parallel to elucidate the mechanism of HA-mediated membrane fusion. Furthermore, the structural organization of HIV gp160, which is directly responsible for cell entry, is similar to HA. Thus, the effort also involves the understanding of the function of HIV gp160.
Transmembrane signal transduction
Every living cell possesses the ability to respond to external signals. Specific receptor proteins in cell membranes recognize light, nutrients, odorants, hormones, and neurotransmitters in order to initiate specific physiological responses in cells. It is remarkable that many functionalre ceptors share the basic structural organization. Thus, each class of receptors might as well have a common signalling mechanism. The primary step in signal transduction is the dynamic response of the receptor which converts a chemical stimulus to a structural message and then transduce it across the membrane through a proper conformational change. Our objective is to define and characterize motion of structural units in the receptor that constitutes transmembrane signal transmission. In our laboratory, the signaling of the bacterial aspartate chemotaxis receptor is studied using spin labeling EPR techniques.
Selected Publications (click for full entry)