My laboratory investigates the structure and function of biological systems using many tools and methods, always with a strong physical perspective. Three interconnected themes are being pursued.

First, we have a long-standing interest in the mechanism of light-driven, long-distance electron transfer in photosynthetic reaction centers, one of the fastest known reactions. This is being studied by femtosecond fluorescence and transient absorption spectroscopy, manipulation in electric fields, site-specific mutagenesis and some novel types of Stark spectroscopy we have developed and applied to many types of molecules. Related methods are also being used to probe excited state dynamics, solvation, and electronic structure in variants of green fluorescent protein (GFP), widely used in cell biology.

Second, we are broadly interested in electrostatics in proteins and how electrostatics affect function. Our current work uses vibrational probes whose sensitivity to electric fields can be calibrated by Stark spectroscopy. Vibrational Stark experiments are particularly useful as they provide a calibration for mapping electrostatic fields in proteins. Probes are introduced on inhibitors, by modification of amino acids and by incorporation of unnatural amino acids.

The third major area of interest involves the use of supported lipid bilayers as mimics for cell surfaces and as tools in biotechnology. A broad vision is to engineer interfaces between hard surfaces and soft materials, ultimately leading to sophisticated biocompatible interfaces that can be used to control, interrogate or organize complex living systems. We have developed methods for partitioning and manipulating the composition and organization of these unique self-assembled systems. Recent work addresses the formation of domains and protein associations with these domains, interactions of DNA, proteins and cells with supported bilayers, and the mechanism of vesicle fusion, both to solid supports and mediated by proteins. This work has motivated the development of advanced optical microscopy methods for probing the interface between membranes on solid supports and cell membranes, potentially with nm vertical resolution. A novel type of imaging mass spectrometry is being applied to characterize the lateral organization and composition of bilayers and associated membranes with 50 nm resolution.

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1) "Kinetics of DNA-mediated docking reactions between vesicles tethered to supported lipid bilayers," Y-H.M. Chan, P. Lenz, S.G. Boxer, Proceedings of the National Academy of Sciences, 104, 18913-18918 (2007).

2) "Anomalous Negative Fluorescence Anisotropy in Yellow Fluorescent Protein (YFP 10C): Quantitative Analysis of FRET in YFP Dimers", Xi. Shi, J. Basran, H.E. Stewart, W. Childs, C.R. Bagshaw, S.G. Boxer, Biochemistry, 46, 14403-14417 (2007).

3) "Controlling Two-dimensional Tethered Vesicle Motion Using an Electric Field: Interplay of Electrophoresis and Electro-osmosis", C. Yoshina-Ishii and S. G. Boxer", Langmuir, 22 , 2384-2391 (2006) .

4) "High Yield of M-Side Electron Transfer in Mutants of Rhodobacter capsulatus Reaction Centers Lacking the L-side Bacteriopheophytin", J. Chuang, Steven G. Boxer, D. Holten and C. Kirmaier, Biochemistry,45, 3845-3851 (2006).

5) "Electric Fields at the Active Site of an Enzyme: Direct Comparison of Experiment with Theory", I. Suydam, C. D. Snow, V. S. Pande and S. G. Boxer, Science, 313, 200-204 (2006).

6) "Site-Specific Conversion of Cysteine Thiols into Thiocyanate Creates an IR Probe for Electric Fields in Proteins," A. T. Fafarman, L. J. Webb, J. I. Chuang, and S. G. Boxer, Journal of the American Chemical Society, 128, 13356-13357 (2006).

7) "Phase Separation of Lipid Membranes Analyzed with High-Resolution Secondary-Ion Mass Spectrometry", M. L. Kraft, P. K. Weber, M. L. Longo, I. D. Hutcheon, S. G. Boxer, Science, 313, 1948-1951 (2006).