Covalent bond formation caught in a LOV photoreceptor
Light-oxygen-voltage (LOV) domains are blue-light photoreceptors of plants, algae and fungi, and among the most widely used tools in optogenetics. They switch on by forming a covalent thioether bond between a conserved cysteine and their flavin chromophore, in a reaction that needs a proton to cross from the cysteine to the flavin through a pocket containing essentially no water. Its mechanism…
Covalent bond formation within a LOV photoreceptor has been observed, shedding light on its mechanism after two decades of debate. By employing 10 time-resolved serial femtosecond crystallography snapshots, infrared spectroscopy, and QM/MM calculations, scientists have resolved the sequence of events at an unprecedented 1.4 Angstrom resolution.
The process begins with the excitation of the flavin chromophore, causing distortion of its ring structure within just 10-100 picoseconds. Following this, hydration of a surface channel occurs over a span of 10 nanoseconds. Subsequently, a single ordered water molecule reaches the active site, transitioning between conformations as the reactive cysteine shifts (100-500 nanoseconds).
At this point, a half-formed thioether bond is captured at one second, with half of the molecules reacting and the other half remaining poised, while the full bond is formed within 10-100 seconds.
The key to this accelerated reaction lies in the involvement of a water molecule that bridges the cysteine and flavin, reducing the barrier from approximately 35 to 15 kcal/mol. This enhancement accelerates the reaction by roughly fourteen orders of magnitude, reducing the half-life from around 237,000 years to a mere fraction of a second.
Notably, the water molecule departs before the bond fully forms. This catalytic strategy, where proteins transiently hydrate and dehydrate active sites on demand, transcends beyond photoreceptors and could have implications for broader protein function.
Written by urgent.news from bioRxiv's reporting — not their text. Machine-written — it may contain errors, so check the original before relying on it.
