Gardner Lab: Light-dependent bacterial signaling pathways

Survival requires organisms to detect and adapt to changes in their surrounding environment. At the molecular level, these processes are achieved by a cascade of interactions among proteins forming signaling transduction pathways. Canonical examples of this principle are provided by bacterial two-component systems (TCS), signaling pathways most simply composed of histidine kinases (HK) and response regulators (RR). Stimuli sensed by the HKs regulate their activation and subsequent phosphorylation of the receiver domain (REC) of downstream RRs, leading to changes in cellular physiology. While numerous proteins involved in two component systems are known, very little is known about the molecular mechanisms that allow these molecules to operate.

Within this context, our group studies HKs which sense blue light to both understand their natural signaling characteristics and to lay the foundation for their use in artificial signaling networks. To become sensitized to blue light, these enzymes contain a HK domain coupled with a N-terminal photosensory Light-Oxygen-Voltage (LOV) domain. Prior studies with LOV domains show that blue light initiates signaling by generating a covalent protein/FMN adduct within the LOV domain core. Nonetheless, the mechanism of signal propagation from the sensory domain to the kinase domain is not entirely clear. Our main goal is to study how the LOV-HK proteins interact, how this interaction can be modulated by light to perturb kinase activity, and evaluate what effect this has on phosphotransfer to downstream response regulators. Using our expertise in nuclear magnetic resonance, X-ray crystallography, biochemistry and other methods has let us begun to address those goals and to characterize how LOV-HKs function in complex signaling pathways (Correa et al., 2013; Rivera-Cancel et al., 2014; Ocasio et al., 2015). Results obtained in our studies not only shed light in many aspects of basic research on light regulated signaling pathways, but also advance the development of light regulated biotechnological tools with direct impact on society.

References

Correa, F., Ko, W.-H., Ocasio, V., Bogomolni, R.A. and Gardner, K.H. (2013) Blue light regulated two-component systems: Enzymatic and functional analysis of light-oxygen-voltage (LOV)-histidine kinases and downstream response regulators. Biochemistry, 52: 4656-4666.

Rivera-Cancel, G., Ko, W-H., Tomchick, D.R., Correa, F. and Gardner, K.H. (2014) Full-length structure of a monomeric histidine kinase reveals basis for sensory regulation. Proc. Natl. Acad. Sci USA, 111: 17839-17844.

Ocasio, V., Correa, F. and Gardner, K.H. (2015) Ligand-induced folding of a two component signaling receiver domain. Biochemistry, 54: 1353-1363.

Contact: Kevin Gardner