Estimation of the available free energy in a LOV2-Jα photoswitch

Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-8816, USA.
Nature Chemical Biology (Impact Factor: 13). 09/2008; 4(8):491-7. DOI: 10.1038/nchembio.99
Source: PubMed


Protein photosensors are versatile tools for studying ligand-regulated allostery and signaling. Fundamental to these processes is the amount of energy that can be provided by a photosensor to control downstream signaling events. Such regulation is exemplified by the phototropins--plant serine/threonine kinases that are activated by blue light via conserved LOV (light, oxygen and voltage) domains. The core photosensor of oat phototropin 1 is a LOV domain that interacts in a light-dependent fashion with an adjacent alpha-helix (J alpha) to control kinase activity. We used solution NMR measurements to quantify the free energy of the LOV domain-J alpha-helix binding equilibrium in the dark and lit states. These data indicate that light shifts this equilibrium by approximately 3.8 kcal mol(-1), thus quantifying the energy available through LOV-J alpha for light-driven allosteric regulation. This study provides insight into the energetics of light sensing by phototropins and benchmark values for engineering photoswitchable systems based on the LOV-J alpha interaction.

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    • "When expressed alone, these STIM1-CT fragments are capable of eliciting varying degrees of constitutive activation of ORAI1 channels to mediate Ca 2+ entry from the extracellular space to the cytosol (Yuan et al., 2009; Park et al., 2009; Zhou et al., 2010a; Soboloff et al., 2012). In the dark, the C-terminal Ja helix docks to the LOV2 domain (Harper, 2003; Yao et al., 2008; Wu et al., 2009) and keeps the ORAI1-activating STIM1-CT fragments quiescent. Upon blue light illumination, photoexcitation generates a covalent adduct between LOV2 residue C450 and the cofactor FMN (Figure 1—figure supplement 1d), thereby promoting the undocking and unwinding of the Ja helix to expose the STIM1-CT fragments. "
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