MpeQ family

The mpeQ gene is present in the "PEII subregion" of the "phycobilisome rod gene region" of all PEII-containing marine Synechococcus strains belonging to pigment types 3c and 3dB (Grébert et al. 2021, 2022); it is found at the same position as mpeY in pigment types 3a and 3dA (Grébert et al. 2021, 2022). MpeQ is related to MpeY, MpeW and MpeZ, and more distantly related to CpeY. It was biochemically characterized as a PEB:Cys-83 alpha-PEII lyase-isomerase in the pigment 3dB Synechococcus strain A15-62 (Grébert et al. 2021). In Synechococcus pigment type 3c strains, this site constitutively binds a PUB, whereas in pigment type 3dB strains, this site binds a PUB in blue light and a PEB in green light, as the result of a competition between the constitutively expressed mpeQ gene and the PEB lyase gene mpeW, which is strongly activated in green light but repressed in blue light (Humily et al. 2013; Grébert et al. 2021). The crystal structure of MpeQ has been described at 2.5-Å resolution and its "question mark" architecture is representative of all members of the E/F clan. (Kumarapperuma et al. 2022).