Rotation of Single Cell Surface Protein Molecules Studied via Nanoparticle Probes

Colorado State University, Fort Collins CO

Investigators

Abstract

Modern optical methods have allowed researchers to determine many properties of single biological molecules, including those on the surfaces of living cells. Evaluating how two molecules of the exact same type can differ in their behavior has enhanced understanding of cellular function. However, one important property of individual molecules, their rates of rotation, has so far escaped characterization since this rotation is extremely rapid, occurring in thousandths of a second or less. Nonetheless rotation of cell surface molecules, particularly proteins, is important since changes in these motions reflect how cells obtain information from their environment. Nanotechnology has recently provided a variety of tags that can be attached to cell surface molecules to provide optical signals from individual biomolecules. This project will employ two of these, nanometer sized cylindrical gold nanorods and eggshaped fluorescent structures called quantum dots, to determine time-dependent orientational changes, and hence rotation rates, of the individual molecules to which they are attached. These single-molecule results will be applied to questions that previous measurements averaging properties of large numbers of molecules together have left unresolved. An example, one such question concerns the actual sizes of large cell surface molecular complexes that initiate particular biological effects. Broader impacts This project will provide Ph.D. educational opportunities to minority, first-generation and female college students in a laboratory that already trains a diverse group of scientists. This group has included women, under-represented minority individuals and first-generation and non-traditional college students at the undergraduate, graduate and postdoctoral levels. The project activities will broaden the exposure of students and trainees to important contemporary topics such as nanotechnology and singlemolecule biophysics. Instrumental resources developed through the project will be available to visiting scientists and to undergraduate researchers and will provide a significant infrastructural resource for biological research, in particular, unique facilities for measuring motions of biological molecules. Such studies will, as have previous investigations by this laboratory, lead to specialized sessions at the U.S. Biophysical Society meetings, short courses in international locations, and laboratory modules in optical biophysical methods for university students. One societal benefit of the project will be improved understanding of mechanisms limiting reproductive efficiency of livestock since one of the topics to be addressed arises from unresolved questions in this area.