Department of Biology
Krieger School of Arts & Sciences
M.Sc. (Diplom) 2001, Leibniz University Hannover, Germany
Ph.D. (Dr. rer. nat.) 2006, Max Planck Institute of Biochemistry, Martinsried, Germany
205 Mudd Hall
3400 N. Charles Street
Baltimore, MD 21218
Protein biogenesis involves a great variety of molecular machines. We use a combination of biochemistry and single-molecule biophysics approaches to study these machines and learn how they help proteins reach and maintain their functional structures. The ultimate goal is to determine the mechanisms that govern protein biogenesis and folding, and to understand how these processes are tuned and coordinated in the cell.
Cellular proteins are synthesized by the ribosome. The ribosome is a very large molecular machine that decodes the genetic information and synthesizes polypeptides, one amino acid at a time. The newly synthesized polypeptide must fold into its native structure to become functionally active. Folding is usually quite fast and begins before synthesis is complete. At the same time, folding to the native structure typically involves the entire sequence of a given protein. This raises the question how synthesis and folding are tuned and coordinated. It is known that modulating synthesis rates affects folding, but it has been very difficult to actually measure folding during synthesis. In addition, we know that a large class of proteins, called molecular chaperones, are essential for proper nascent protein folding in the cell, but how they operate remains poorly understood. We have recently developed an experimental system to study folding on the ribosome using optical tweezers. We are now using this system to follow the synthesis and folding of nascent polypeptides in real-time to reveal how hey are coordinated. We are also interested in learning how molecular chaperones interact with the ribosome and with nascent polypeptides and how they contribute to efficient folding and cellular fitness.
While virtually all proteins are synthesized in the cytosol, many of them are targeted to other cellular compartments and must cross a membrane to reach their final destination. The lipid bilayers that demarcate the cytosol are impermeable to proteins but contain transport systems that enable protein export. We are developing single-molecule approaches for studying the machines and processes involved the translocation of polypeptides across membranes. This will open exciting new avenues for studying membrane proteins with single-molecule biophysics approaches.
Goldman, D.H.*, Kaiser, C.M.*#, Milin, A., Righini, M., Tinoco Jr., I., and C. Bustamante. #Mechanical force releases nascent chain-mediated ribosome arrest in vitro and in vivo. Science. In press.
*equal contributions #corresponding authors
Bustamante, C., Kaiser, C.M., Maillard, A.R., Goldman, D. and C. Wilson. (2014) Mechanisms of cellular proteostasis: Insights from single molecule approaches. Annu Rev Biophys 43, 119-40.
Kaiser, C.M., P. Bujalowski, L. Ma, J. Anderson, H.F. Epstein, and A.F. Oberhauser. (2012) Tracking UNC-45 chaperone-myosin interaction with a titin mechanical reporter. Biophys. J. 102:2212-2219.
Kaiser, C.M., D. Goldman, J. Chodera, I. Tinoco, and C. Bustamante. (2011) The ribosome modulates nascent protein folding. Science 344:1723-1727.
Maillard, A.R., G. Chistol, M. Sen, M. Righini, J. Tan, C.M. Kaiser, C. Hodges, A. Martin, and C. Bustamante. (2011) ClpX generates mechanical force to unfold and translocate its protein substrates. Cell 145:459-469.
Lakshmipathy, S. K., Tomic, S., Kaiser, C. M., Chang, H. C., Genevaux, P., Georgopoulos, C., Barral, J. M., Johnson, A. E., Hartl, F. U. and S.A. Etchells. (2007) Identification of nascent chain interaction sites on trigger factor. J Biol Chem 282, 12186-93.
Kaiser, C.M., H.C. Chang, V.R. Agashe, S.K. Lakshmipathy, S.A. Etchells, M. Hayer-Hartl, F.U. Hartl, and J.M. Barral. (2006) Real-time observation of trigger factor function on translating ribosomes. Nature 444:455-460.