Fig. 3: Splitting of the core subunit PsaA in C. velia and comparative analysis with the PsaA homologue from Symbiodinium. | Nature Communications

Fig. 3: Splitting of the core subunit PsaA in C. velia and comparative analysis with the PsaA homologue from Symbiodinium.

From: The cryo-EM structure of Photosystem I from Chromera velia with a bound superoxide dismutase heterodimer

Fig. 3

a The secondary structure of PsaA1 and PsaA2 is shown and numbered from the N- to the C-terminus: transmembrane helices (TMH), helices (H), and β-strands (B). Note the partially disordered N-terminus near the ferredoxin-binding site. b The shifted TMH2 helix, accompanied by a truncation of the subsequent loop by ~8 Å, is depicted. The lower-resolution density, indicative of local flexibility of this helix, is displayed as a transparent isosurface representation. c Several structural remodelings are observed: the loop between β-sheets B3 and B4 is truncated, while the loop region between TMH3 and B1 is remodeled into two newly formed helices, H3 (α) and H4 (3₁₀). The new C-terminus is redirected toward FCPa, where it stabilizes attachment to the PSI core through a newly formed inter-subunit β-sheet and a salt bridge between R277 of PsaA1 and D214 of FCPa.

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