Molecular Mechanisms of Activation in the Orange Carotenoid Protein Revealed by Molecular Dynamics

Abstract

Light-harvesting in photosynthesis is accompanied by photoprotective processes. In cyanobacteria, the photoprotective role is played by a specialized complex, the orange carotenoid protein, which is activated by strong blue-green light. This photoactivation involves a unique series of structural changes which terminate with an opening of the complex into two separate domains, one of which acts as a quencher for the lightharvesting complexes. Many experimental studies have tried to reveal the molecular mechanisms through which the energy absorbed by the carotenoid finally leads to the large conformational change of the complex. Here, for the first time, these mechanisms are revealed by simulating at the atomistic level the whole dynamics of the complex through an effective combination of enhanced sampling techniques. On the basis of our findings, we can conclude that the carotenoid does not act as a spring that, releasing its internal strain, induces the dissociation, as was previously proposed, but as a "latch" locking together the two domains. The photochemically triggered displacement of the carotenoid breaks this balance, allowing the complex to dissociate.

General method to stabilize mesophilic proteins in hyperthermal water

“…The structure-function relationship of amphiphilic polymers and their thermal stabilization effect was investigated. All-atom classical molecular dynamics (MD) simulations of complexes (BSA with and without PEG or/and C 18 fragment, respectively) were performed in Amber18 package to study the stability of protein backbone under the different temperatures ( Bondanza et al., 2020 ; Jia et al., 2020 ). Final 100 ns trajectories were used for further analysis.…”

A synthetic switch based on orange carotenoid protein to control blue light responses in chloroplasts

“…1B). Since the strength of these interactions depends on the light‐dependent translocation of the keto‐carotenoid inside the OCP2 structure (Gupta et al , 2015; Leverenz et al , 2015; Bondanza et al , 2020), we expected the NTD and the CTD to associate in the dark, whereas exposure to blue‐green light would bring them apart.…”

“…The OCP apoprotein non‐covalently incorporates a single keto‐carotenoid molecule, such as canthaxanthin, 3’‐hydroxyl‐echinenone or echinenone, as prosthetic group buried inside the two domains (Punginelli et al , 2009). OCP photoactivation is accompanied by extensive reconfiguration of carotenoid‐protein interactions, with the consequent translocation of the pigment within the protein (Gupta et al , 2015; Leverenz et al , 2015; Bondanza et al , 2020). Photoconversion is possible only when a keto‐carotenoid is buried inside the protein, whilst association with other carotenoids inhibits its photoconversion ability (Punginelli et al , 2009; Wilson et al , 2011).…”

A Favorable Path to Domain Separation in the Orange Carotenoid Protein

“…Bondanza et al has also studied OCP domain dissociation prior to and subsequent to carotenoid translocation into the NTD. 25 Although their study produced a domain 2D-to-1D projection is described by Eq. 2 in the Method section.…”