A Favorable Path to Domain Separation in the Orange Carotenoid Protein

SHARAWY, MAHMOUD; PIGNI, NATALIA B.; MAY, ERIC R.; GASCÓN, JOSÉ A.

PROTEIN SCIENCE

JOHN WILEY & SONS INC

Año: 2022

0961-8368

he Orange Carotenoid Protein (OCP) is responsible for nonphotochemical quenching (NPQ) in cyanobacteria, a defense mechanism against potentially damaging effects of excess lightconditions. This soluble two-domain protein undergoes profound conformational changes uponphotoactivation, involving translocation of the ketocarotenoid inside the cavity followed bydomain separation. Domain separation is a critical step in the photocycle of OCP because itexposes the N-terminal domain (NTD) to perform quenching of the phycobilisomes. Manydetails regarding the mechanism and energetics of OCP domain separation remain unknown. Inthis 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 canthaxanthinhas a profound effect on the energetic landscape and that domain separation only becomesfavorable following translocation. We further explore, characterize, and validate the free energy