Time-resolved Studies of Photosensors
Photoactive Yellow Protein
Photoactive yellow protein (PYP) is a member of the Xanthopsin family of eubacterial photoreceptors. PYP is a 14 kDa cytosolic protein that has a characteristic bright yellow color with an absorbance maximum at 446nm. A 4-hydroxyl cinnamic acid chromophore is covalently attached to Cys69 through a thioester bond. Structurally, PYP is a member of the PER-ARNT-SIM (PAS) superfamily, a diverse group of signaling proteins. Cellularly, this protein is thought to be a blue light photoreceptor involved in negative phototaxis. PYP has been embraced as a tractable system in which to investigate signal transduction at the molecular level. Absorption of visible light by the chromophore initiates a photocycle involving a sequence of intermediates, each with a unique optical absorption maximum. The structures of these photocycle intermediates are being investigated using time-resolved Laue crystallography with the goal of determining how absorption of a single photon translates into structural change and cellular signaling.
|Phototropin and phy3|
|The phototropins (phot1 and phot2) are plant blue-light photoreceptors that control phototropism, light-mediated chloroplast movement, and stomatal opening. These photoreceptors exhibit blue light-dependent autophosphorylation and contain two flavin-binding light, oxygen, or voltage (LOV) domains and a serine/threonine kinase domain. LOV domains, like PYP, are members of the PAS superfamily. Each LOV domain non-covalently binds a single FMN molecule and exhibits reversible photochemistry in vitro when expressed separately or in tandem. This lab has recently determined the dark- and photoexcited-state crystal structures of the LOV2 domain from the phototropin portion of Adiantum (maidenhair fern) phy3. Additional experiments on phototropin are underway with the end goal of understanding the structural and chemical nature of sensing and signaling during plant photomorphogenesis.|
|Time-resolved studies of heme proteins
Time-resolved Laue work on the heme protein myoglobin is a long-standing interest of this lab. Research on this system continues as we work to understand the kinetics and pathways of ligand dissociation and rebinding with the heme after laser photolysis.
FixL is a sensor kinase involved in redox sensing in nitrogen fixing Rhizobia. The protein contains a single N-terminal PAS domain and a C-terminal histidine kinase. The sensor portion of this protein is the PAS domain which contains a single molecule of heme. Work is in progress on this heme-binding PAS domain.
Development of improved methods in Laue data collection and analysis are key to the success of time-resolved experiments. A current focus of the group is extraction of single structural intermediates from a Laue diffraction time series.
Cryocrystallograpy and Radiation Damage
The effects of crystal freezing and radiation damage on data quality from macromolecular crystals is an active area of research in the Moffat Lab.