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B.S. 1974, Michigan State University
Ph.D. 1979, University of California, Berkeley
Postdoctoral Fellow at University of Colorado
Richard J. Burke Professor of Chemistry
Quantitative fluorescence microscopy in vivo and in vitro
We participate in the revolution in fluorescence microscopy of biological systems. It is now possible to measure the spatial distribution of proteins and DNA loci with 30-nm precision in live cells and to track their motion in real time. The result is an unprecedented, high resolution view of biological structure and activity. Areas of current interest include: (1) The motion and spatial distribution of GFP-labeled species in live E. coli cells. Species of interest include RNA polymerase, ribosomes, architectural proteins, and specific DNA loci. The transcription/translation machinery (ribosomes, the nucleoid, and RNAP) all exhibit a remarkable level of spatial organization. (2) The time-resolved attack of antimicrobial agents on single bacterial cell membranes. Examples include LL-37, a human antimicrobial peptide, and synthetic random copolymers designed by the Gellman group. Simultaneous two-color imaging of the antimicrobial and cytoplasmic or periplasmic GFP yields unprecedented insight into the mechanism of attack. (3) The spatial distribution and function of proteins in the tomasyn family, mutations in which are believed to be important factors in Type-2 diabetes.
|Fig. 2. RNAP image in live E. coli (inset) and time-dependent recovery of the fluorescence asymmetry after one lobe is photobleached. Blue line is pre-bleach value.|
The ribosomes, the nucleoid, and RNAP all exhibit a remarkable level of time-varying spatial organization. Simple “toy models” developed with the Yethiraj group may help understand the organization based on excluded volume and entropic effects alone (Fig. 4).
(3) The time-resolved attack of antimicrobial agents on bacterial cell membranes. Examples include LL-37 (Fig. 5), a human antimicrobial peptide, and synthetic random copolymers designed by the Gellman group. Simultaneous two-color imaging of the antimicrobial and cytoplasmic or periplasmic GFP yields unprecedented insight into the mechanism of attack.
Periplasmic GFP and rhodamine-LL-37 images vs time. Axial intensity plots at right. The attack comes as three waves, the second of which spreads outward from mid-cell and lyses the outer membrane, releasing GFP.
Awards and Honors
|Fellow, American Association for the Advancement of Science||2009|
|Fellow, American Physical Society||2001|
|Hilldale Undergraduate/Faculty Research Awards, 1993, 1995, 1999, 2001, 2002 (with undergraduates K. Haug , W.-K. Woo, V. Chen, T. Huppert, L. Klein)||2002|
|Vilas Associate Award, UW-Madison||1997|
|Evan P. Helfaer Professor of Chemistry||1996|
|Low-frequency Torsional and Vibrational Motions in Toluene+, Phenylsilane+, and Benzyl+: Experiments and Ab Initio Calculations. In: . High Resolution Laser Photoionization and Photoelectron Studies. New York, NY: Wiley; 1995. pp. 331-367..|
|Rigidification of the Escherichia coli cytoplasm by the human. Proceedings of the National Academy of Sciences of the United States Of. 2019;116:1017-1026..|
|Near Saturation of Ribosomal L7/L12 Binding Sites with Ternary Complexes in Slowly Growing E. coli. Journal of Molecular Biology. 2019;431:2343-2353..|
|Resistance of early stationary phase E. coli to membrane permeabilization by the antimicrobial peptide Cecropin A. Biochimica Et Biophysica Acta-Biomembranes. 2019;1861..|
|Melittin-Induced Permeabilization, Re-sealing, and Re-permeabilization of E-coli Membranes. Biophysical Journal. 2018;114:368-379..|