Wiener, Michael C.
Professor, Molecular Physiology and Biological Physics
- BS, Physics, University of Rochester
- PhD, Physics & Biophysics, Carnegie Mellon University
- Postdoc, Membrane Diffraction, University of California, Irvine
- Postdoc, Protein Cystallography, University of California, San Francisco
Structural biology (esp. crystallography) of integral membrane proteins; TonB-dependent active transport across the bacterial outer membrane; cancer-related membrane proteins; crystallization methods development
The structure/function paradigm is of central import in modern molecular biology. High-resolution structures, determined by x-ray crystallography, of proteins involved in biological processes provide insight into their function. These structures provide a basis for the design of future experiments to probe more deeply the precise molecular mechanisms that underlie biological activity. In addition to providing fundamental insight into function and mechanism, structures of proteins involved in disease and other pathophysiological states can serve as targets for structure-based drug design.
We propose a structure-based approach to the determination of membrane protein function. Our goal is to solve x-ray crystal structures of channel, transport and receptor proteins, and to use these structures in conjunction with other results to understand the molecular basis of function. While thousands of soluble protein structures have been solved (at a rate of about three per day!), very few integral membrane proteins have been solved to high resolution. Major technical, scientific and intellectual challenges involved include: expression of multimilligram quantities of recombinant protein for crystallization experiments, crystallization from detergent-solubilized protein solutions where the properties of the detergent may be as or more significant than those of the protein, and determination of a structure from crystals that may not be of very high quality. The 'payoff' of this research endeavor, however, is large; the structure of a membrane protein at atomic (or near-atomic) resolution is a significant achievement.
In addition to structure determination, there are research opportunities in the lab for the utilization or development of expression systems, and for biophysical studies of membrane protein crystallization. A range of proteins are under consideration for study, either alone or in collaboration with other investigators in or outside of the university. Many of these are of major biological and/or medical interest. Some of the current projects in my laboratory include:
1. The Molecular Basis of Protein-Mediated Water Transport
Protein-mediated water transport is a fundamental physiological process in all organisms. It is carried out by integral membrane proteins, aquaporins, that function as water channels. Aquaporins serve as passive, diffusion-limited channels to dissipate osmotic gradients that form across cell membranes. Currently, six different human aquaporins have been discovered, each with a different distribution in bodily organs, tissues and cells. This heterogeneous distribution predicts significant roles for human aquaporins in both normal physiology and disease. Mutations in one aquaporin, aquaporin-2, are responsible for nephrogenic diabetes insipidus. Others are implicated in the maintenance of water homeostasis in erythrocytes, kidney, lung, brain and salivary gland. The aquaporins are likely targets for the future development of therapeutic agents directed to prevention or control of edema and fluid balance. Crystals of human aquaporin-1 have been obtained, and structure determination is underway.
2. Structural Dissection of Bacterial Active Transport Pathways
Bacteria possess active transport pathways for the binding and uptake of essential compounds that they do not themselves make biosynthetically. These pathways consist of an outer membrane receptor which binds substrate with high specificity and affinity, and a complex of proteins in the inner membrane. One of these inner membrane proteins spans the periplasmic space and functions to couple the transmembrane potential of the inner membrane to drive transport across the outer membrane. Overexpression, purification and crystallization of the vitamin B12 receptor BtuB is underway, in collaboration with Prof. Robert Kadner of the Microbiology Department. Other proteins in this pathway will also be examined structurally, alone or in complex with the receptor.
These transport pathways are also utilized by bacterial protein toxins (bacteriocins) and bacteriophage to gain entry into the target cell. One class of bacteriocins are the channel-forming colicins, which bind to specific outer membrane receptors, translocate across the outer membrane and form voltage-gated channels in the inner membrane. These various functions are performed by different domains of the protein. A single colicin molecule is sufficient to kill a bacterium, and thus are both more selective and effective than conventional antibiotics. We solved the structure of the soluble form of colicin Ia.
List of Publications in Pubmed