8K9E

Cryo-EM structure of the photosynthetic alternative complex III from Chloroflexus aurantiacus at 3.3 angstrom

Summary for 8K9E

• Entry DOI: 10.2210/pdb8k9e/pdb
• EMDB information: 36984
• Descriptor: Cytochrome c7-like domain-containing protein, IRON/SULFUR CLUSTER, FE3-S4 CLUSTER, ... (15 entities in total)
• Functional Keywords: photosynthetic alternative complex iii, membrane protein
• Biological source: Chloroflexus aurantiacus (strain ATCC 29366 / DSM 635 / J-10-fl); More
• Total number of polymer chains: 8
• Total formula weight: 307153.68

Authors

Xu, X. (deposition date: 2023-08-01, release date: 2024-03-06)

Primary citation

Xin, J.,Min, Z.,Yu, L.,Yuan, X.,Liu, A.,Wu, W.,Zhang, X.,He, H.,Wu, J.,Xin, Y.,Blankenship, R.E.,Tian, C.,Xu, X.
Cryo-EM structure of HQNO-bound Alternative Complex III from the anoxygenic phototrophic bacterium Chloroflexus aurantiacus.
Plant Cell, 2024

PubMed Abstract: Alternative complex III (ACIII) couples quinol oxidation and electron acceptor reduction with potential transmembrane proton translocation. It is compositionally and structurally different from the cytochrome bc1/b6f complexes, but functionally replaces these enzymes in the photosynthetic and/or respiratory electron transport chains (ETCs) of many bacteria. However, the true compositions and architectures of ACIIIs remain unclear, as do their structural and functional relevance in mediating the ETCs. We here determined cryogenic electron microscopy structures of photosynthetic ACIII isolated from Chloroflexus aurantiacus (CaACIIIp), in apo-form and in complexed form bound to a menadiol analog 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO). Besides six canonical subunits (ActABCDEF), the structures revealed conformations of two previously unresolved subunits, ActG and I, which contributed to the complex stability. We also elucidated the structural basis of menaquinol oxidation and subsequent electron transfer along the [3Fe-4S]-6 hemes wire to its periplasmic electron acceptors, using electron paramagnetic resonance (EPR), spectroelectrochemistry, enzymatic analyses and molecular dynamics (MD) simulations. A unique insertion loop in ActE was shown to function in determining the binding specificity of CaACIIIp for downstream electron acceptors. This study broadens our understanding of the structural diversity and molecular evolution of ACIIIs, enabling further investigation of the (mena)quinol oxidoreductases evolved coupling mechanism in bacterial energy conservation.

PubMed: 38299372
DOI: 10.1093/plcell/koae029

Experimental method

ELECTRON MICROSCOPY (3.33 Å)