Fig. 2. Cryo-EM structure of A. panamensis PSI.

(A) Structure of the trimeric A. panamensis PSI complex viewed from the stromal side. Cofactors except Chls are hidden for clarity, and those are shown as tetrapyrrole rings only. Note that the PsaK and PsaX subunits found in PSI complexes from some other cyanobacterial species are not present in A. panamensis. Their locations relative to other PSI structures are designated by the letters K and X in red circles. (B) Model within the sharpened map showing the vicinity of P700 which is composed of the P_A (a Chl a' molecule) and P_B (a Chl a molecule). (C) Model within the sharpened map showing the vicinity of F_X (a [4Fe-4S] cluster), A_1B (a menaquinone-4 molecule), and nearby waters (red spheres). (D) Model within the unsharpened map of PsaI that was previously suggested not to be found in A. panamensis. (E) Model within the unsharpened map of PsaJ that was previously suggested not to be found in A. panamensis.