Binding of red form of Orange Carotenoid Protein (OCP) to phycobilisome is not sufficient for quenching

Publication date: Available online 11 January 2020Source: Biochimica et Biophysica Acta (BBA) - BioenergeticsAuthor(s): Wenjing Lou, Dariusz M. Niedzwiedzki, Ruidong J. Jiang, Robert E. Blankenship, Haijun LiuAbstractThe Orange Carotenoid Protein (OCP) is responsible for photoprotection in many cyanobacteria. Absorption of blue light drives the conversion of the orange, inactive form (OCPO) to the red, active form (OCPR). Concomitantly, the N–terminal domain (NTD) and the C–terminal domain (CTD) of OCP separate, which ultimately leads to the formation of a quenched OCPR–PBS complex. The details of the photoactivation of OCP have been intensely researched. Binding site(s) of OCPR on the PBS core have also been proposed. However, the post–binding events of the OCPR–PBS complex remain unclear. Here, we demonstrate that PBS–bound OCPR is not sufficient as a PBS excitation energy quencher. Using site–directed mutagenesis, we generated a suite of single point mutations at OCP Leucine 51 (L51) of Synechocystis 6803. Steady–state and time–resolved fluorescence analyses demonstrated that all mutant proteins are unable to quench the PBS fluorescence, owing to either failed OCP binding to PBS, or, if bound, an OCP–PBS quenching state failed to form. The SDS–PAGE and Western blot analysis support that the L51A (Alanine) mutant binds to the PBS and therefore belongs to the second category. We hypothesize that upon binding to PBS, OCPR likely reorganizes and adopts a ...

Source: Biochimica et Biophysica Acta (BBA) Bioenergetics - January 12, 2020 Category: Biochemistry Source Type: research