E/F clan

The crystal structure of the heterodimer of CpcE-I/F-I from Nostoc sp. PCC7120 was determined at a 1.89-Å resolution (Zhao et al., 2017; PDB: 5N3U). However, the crescent-shaped architecture described by these authors has recently been disputed after the resolution at 2.5-Å of the structure of the lyase-isomerase MpeQ from Synechococcus sp. A15-62 (Kumaraperruma et al. 2022). The latter authors posit that the E/F family of bilin lyases, including the single-chain and heterodimeric enzymes, share a common structural framework represented by the question-mark architecture of MpeQ (PDB: 7MC4 and 7MCH).