Current limits of structural biology: the transient interaction between cytochrome c and photosystem I

Kölsch, A.; Pieper, J.; Radon, C.; Wendler, P.; Zouni, A.; Lisdat, F.; Mielke, T.; Bürger, J.; Baumert, A.; Feoktystov, A.; Golub, M.

doi:10.1016/j.crstbi.2020.08.003

Journal Article

FZJ-2020-03063

Current limits of structural biology: the transient interaction between cytochrome c and photosystem I

Kölsch, A.Extern* ; Radon, C. ; Golub, M. ; Baumert, A. ; Bürger, J. ; Mielke, T.Extern* ; Lisdat, F. ; Feoktystov, A.FZJ* ; Pieper, J. ; Zouni, A. (Corresponding author) ; Wendler, P. (Corresponding author)

2020
Elsevier Amsterdam

Current research in structural biology 2, 171-179 (2020) [10.1016/j.crstbi.2020.08.003]

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Please use a persistent id in citations: http://hdl.handle.net/2128/25656 doi:10.1016/j.crstbi.2020.08.003

Abstract: Trimeric photosystem I from the cyanobacterium Thermosynechococcus elongatus (TePSI) is an intrinsic membrane protein, which converts solar energy into electrical energy by oxidizing the soluble redox mediator cytochrome c6 (Cyt c6) and reducing ferredoxin. Here, we use cryo-electron microscopy and small angle neutron scattering (SANS) to characterize the transient binding of Cyt c6 to TePSI. The structure of TePSI cross-linked to Cyt c6 was solved at a resolution of 2.9 Å and shows additional cofactors as well as side chain density for 84% of the peptide chain of subunit PsaK, revealing a hydrophobic, membrane intrinsic loop that enables binding of associated proteins. Due to the poor binding specificity, Cyt c6 could not be localized with certainty in our cryo-EM analysis. SANS measurements confirm that Cyt c6 does not bind to TePSI at protein concentrations comparable to those for cross-linking. However, SANS data indicate a complex formation between TePSI and the non-native mitochondrial cytochrome from horse heart (Cyt cHH). Our study pinpoints the difficulty of identifying very small binding partners (less than 5% of the overall size) in EM structures when binding affinities are poor. We relate our results to well resolved co-structures with known binding affinities and recommend confirmatory methods for complexes with KM values higher than 20 μM.

Keyword(s): Polymers, Soft Nano Particles and Proteins (1st) ; Biology (2nd)

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