Associate Professor
Department of Chemical & Biomolecular Engineering
Whiting School of Engineering

oster@jhu.edu

119 Maryland Hall
3400 N. Charles Street
Baltimore, MD 21218

Office: 410-516-7144
Lab: 410-516-4146

The incredible complexity of biological systems derives to a large extent from the high degree of interactions amongst their constituent components. As such, the cell is often described as a complex circuit consisting of an interacting network of molecules. A key component of these networks are protein switches that serve to couple cellular functions. A switch recognizes an input signal (e.g. ligand concentration, pH, covalent modification) and, as a result, its output signal (e.g. enzyme activity, ligand affinity, oligomeric state) is modified. Examples of natural switches include allosteric enzymes which couple effector levels to enzymatic activity and ligand-dependent transcription factors that couple ligand concentration to gene expression. Creating artificial protein switches is an important goal of chemical biology. The ability to create novel switches or to modify existing switches by coupling hitherto uncoupled functions would enable the rewiring of the cellular circuitry to our own design. In addition, the ability to create protein switches has tremendous practical potential for developing novel molecular sensors and as a tool for elucidating molecular and cellular function.

We have developed a general approach for creating switches in which one selects from natural or engineered proteins with the desired input and output functions and, by combining the proteins in a systematic fashion, creates switches in which their functions were tightly coupled. Such an approach is inspired by the evolutionary mechanism of domain recombination – a major facilitator in the natural evolution of protein function. We reasoned that a diverse exploration of fusion geometries between two proteins would enable the creation of switches with superior properties. The structural space that we sought to explore can be conceptualized as rolling the two proteins across each others surface and fusing them through peptide bonds at the points where their surfaces meet. We developed a novel, homology-independent, combinatorial method for recombining genes that samples such a structural space. We have utilized this strategy to combine the enzyme TEM-1 beta-lactamase and the ligand-binding protein maltose binding protein and create a family of allosteric beta-lactamases that are modulated by maltose.

The major goals of our research program on molecular switches are (1) to create protein molecular switches through a combination of chemical and biological approaches that include molecular evolution and protein design, (2) to elucidate the mechanism of the switches created and (3) to develop switches for applications. For example, coupling a ligand-binding protein and a protein with good signal transduction properties would result in the creation of a molecular sensor for the ligand. Furthermore, switches that establish connections between cellular components with no previous relationship can result in novel cellular circuitry and phenotypes. We envision, for example, that such switches might establish connections between molecular signatures of disease (e.g. abnormal concentrations of proteins, metabolites, signaling or other molecules) and functions that serve to treat the disease (e.g. delivery of drugs, modulation of signaling pathways or modulation of gene expression) and therefore possess selective therapeutic properties.

Selected Publications
Sohka, T., R.A. Heins, R.M. Phelan, J.M. Greisler, C.A. Townsend, and M. Ostermeier. (2009) An externally-tunable bacterial band-pass filter. Proc. Nat. Acad. Sci. USA 106:10135-10140.

Liang, J., J.R. Kim, J.T. Boock, T.J. Mansell, and M. Ostermeier. (2007) Ligand binding and allostery can emerge simultaneously. Protein Sci. 16:929-937.

Kim, J.R., and M. Ostermeier. (2006) Modulation of effector affinity by hinge region mutations also modulates switching activity in an engineered allosteric TEM1 beta-lactamase. Arch. Biochem. Biophys. 446:44-51.

Guntas, G., T.J. Mansell, J.R. Kim, and M. Ostermeier. (2005) Directed evolution of protein switches and their application to the creation of ligand-binding proteins. Proc. Nat. Acad. Sci. USA 102:11224-11229.

Paschon, D., Z.S. Patel, and M. Ostermeier. (2005) Enhanced catalytic efficiency of aminoglycoside phosphotransferase (3')-IIa achieved through protein fragmentation and reassembly. J. Mol. Biol. 353:26-37.

Guntas, G., S.F. Mitchell, and M. Ostermeier. (2004) A molecular switch created by in vitro recombination of non-homologous genes. Chem. Biol. 11:1483-1487.