A favorable path to domain separation in the orange carotenoid protein.

Autor: Sharawy M; Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, USA., Pigni NB; Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA.; Instituto de Ciencia y Tecnología de Alimentos Córdoba (ICYTAC-CONICET), Ciudad Universitaria, Córdoba, Argentina., May ER; Department of Molecular and Cell Biology, University of Connecticut, Storrs, Connecticut, USA., Gascón JA; Department of Chemistry, University of Connecticut, Storrs, Connecticut, USA.
Jazyk: angličtina
Zdroj: Protein science : a publication of the Protein Society [Protein Sci] 2022 Apr; Vol. 31 (4), pp. 850-863. Date of Electronic Publication: 2022 Jan 22.
DOI: 10.1002/pro.4273
Abstrakt: The orange carotenoid protein (OCP) is responsible for nonphotochemical quenching (NPQ) in cyanobacteria, a defense mechanism against potentially damaging effects of excess light conditions. This soluble two-domain protein undergoes profound conformational changes upon photoactivation, involving translocation of the ketocarotenoid inside the cavity followed by domain separation. Domain separation is a critical step in the photocycle of OCP because it exposes the N-terminal domain (NTD) to perform quenching of the phycobilisomes. Many details regarding the mechanism and energetics of OCP domain separation remain unknown. In this work, we apply metadynamics to elucidate the protein rearrangements that lead to the active, domain-separated, form of OCP. We find that translocation of the ketocarotenoid canthaxanthin has a profound effect on the energetic landscape and that domain separation only becomes favorable following translocation. We further explore, characterize, and validate the free energy surface (FES) using equilibrium simulations initiated from different states on the FES. Through pathway optimization methods, we characterize the most probable path to domain separation and reveal the barriers along that pathway. We find that the free energy barriers are relatively small (<5 kcal/mol), but the overall estimated kinetic rate is consistent with experimental measurements (>1 ms). Overall, our results provide detailed information on the requirement for canthaxanthin translocation to precede domain separation and an energetically feasible pathway to dissociation.
(© 2022 The Protein Society.)
Databáze: MEDLINE
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