Zebrafish development ● Takes about 3 days from fertilization form embryo to hatch and release larva ● Early cell in embryo is not differentiated but after some point(3.5 hr) there is differentiation ○ Interest to developmental biologist include role of transcription factor ● At some point, cell’s fate is determined ○ Signalling pathway are key ○ Involves phosphorylation of proteins (SMADS) ■ Activates specific genes Light-Oxygen-Voltage(LOV) Photoreceptors ● Light sensitive region found in plant photopsin,bacteria fungi ● FAD undergoes redox reaction ● LOV Domains are flavin-dependent ○ FAD and FMN contain the isoalloxazine ring ○ Linked via ribitol to either phosphate or ADP ● Organisms need to respond to light ○ Photoropsin and circadian rhythms ○ Isoalloxazine ring can respond/react, light oxygen and changes in voltage Isoalloxazine Ring Bends ● Redox states and protein environment affects chemistry and structure ○ Reduction results in sp2 to sp3 hybridization ■ Planar to strained tetrahedral ○ Structure and charge affect redox potential ○ Conversely, redox state can affect structure LOV Domain Response to light ● Light induced covalent reduction of flavin ○ C108 sulfur reacts with C(4a) of isoalloxazine ring ■ Light-induced deprotonation of C108 thiol ■ Stability of cysteninl-4a adduct varies between LOV domains(81s to 5h) ● Structure on left-dark state on right ● Superposed dark(yellow) and light (teal) ■ Light activation leads to dimer