Sandbox Reserved 951: Difference between revisions

It has been found that the reaction between luciferin and CoA is possible, forming in a first step luciferin-AMP and then luciferin-CoA. This reaction leads to an interesting biological phenomenon : when this reaction occurs in parallel of light emission reaction, we don't have a flash of light but a continuous light emission. This is because luciferin-AMP is a competitive inhibitor of the reaction whereas the luciferin-CoA is not. So the inhibition is deleted and the reaction continue to occur.

The active site is not strictly highlighted according to the actual state of studies but some residues and motifs strongly modified have been determined and this conformation enables to find the active site. Many of these conserved residue are located on the core of the β-barrel and on the small C-terminal domain and in the surface of the N-terminal domain, which forms a <scene name='60/604470/Depression_c-ter_and_n-ter/1'>depression</scene>. However, this depression is too large to enable interactions between residues and substrates, so it is thought that a conformational change occurs and sandwiches the substrates, forming the active site. This conformational change provide a suitable environment for light production because of water molecules will be excluded from the active site, favouring intramolecular reactions. Residues also follow a <scene name='60/604470/Cleft/1'>cleft</scene> caused by of the <scene name='60/604470/Beta_sheet_b/3'>Beta-sheet B</scene> against the <scene name='60/604470/Beta_barrel/3'>Beta-barrel</scene>.

[[Image:Luciferin_bounding_to_luciferase.jpg|250px|right|thumb|Hydrogen bonding between Luciferase and substrates luciferin (green), ATP (violet) and Mg2+]]

We find a signal motif in luciferase which is <scene name='60/604470/Atp_binding_signal_motif/1'>[STG]-[STG]-G-[ST]-[ST]-[TSE]-[GS]-x-[PALIVM]-K</scene> where some residue like lysine are always conserved. This pattern enables ATP binding thanks to hydrogen bonds between residues and phosphates of ATP. There is another pattern : <scene name='60/604470/Adenosine_ring_binding/1'>[YFW]-[GASW]-x-[TSA]-E</scene> which takes a particular conformation because of hydrogen bonds between residues and maintain the adenosin ring of ATP.

Luciferase holds the luciferin with the specific residues <scene name='60/604470/Residues_helding_luciferin/1'>arginin 218, phenylalanin 247, serin 347 and adenin 348</scene>, still with hydrogen bounds. This bindings makes the carboxylate oxygen of luciferin points toward the α phosphate of ATP, so the oxygen is well-positionned to attack the α phosphate. This promotes the luciferin-AMP formation.

D-LH2 and (B) arachidonic acid]]

When the pH is low, the color of light changes. This is probably due to the hydrogen bonds network between substrates, residues of the cleft and water. Indeed, this network triggers to an external electrostatic potential which stabilizes a charge created during the reaction of light emission. The lower pH leads to a weakening of the network, so the energy which can be emitted decreases and the wavelength of photon increases and becomes more red.

That is why luciferase is more and more considered as coming from a common ancestor involved in this kind of reaction and the light production would only be a side effect of the reaction.