Insight into the oligomeric structure of PORA from A. thaliana

•POR forms large oligomers before binding of substrates.•Subunits within the oligomer exchange in the minute-range scale.•Catalytic motifs of adjacent subunits become close to each other after binding of substrates.

Light-dependent protochlorophyllide oxidoreductase (POR, E.C. 1.3.1.33) is a plant enzyme that directly needs light to conduct a biochemical reaction. In the present paper we confirmed that POR forms large oligomers in solution before binding of substrates. We carried out the research using different techniques: cross-linking, native gel electrophoresis and FRET measurements. Mass spectrometry analysis of the cross-link products provided the first structural data about the organisation of the oligomer of POR. The results indicated that the catalytic motifs of the adjacent subunits become close to each other upon binding of substrates. Moreover, we identified two mutations of POR that disturbed its oligomerisation properties: Δ85-88 and Δ240-270. Additionally, a complete loss of the catalytic activity was observed for the following mutations: Δ189-194, Δ240-270, Δ318-331 and Δ392-393.