9ILT

Crystal structure of alternative complex III from Chloroflexus aurantiacus

Summary for 9ILT

• Entry DOI: 10.2210/pdb9ilt/pdb
• Descriptor: Cytochrome c7-like domain-containing protein, IRON/SULFUR CLUSTER, FE3-S4 CLUSTER, ... (11 entities in total)
• Functional Keywords: alternative complex iii, chloroflexus aurantiacus, photosynthetic electron transport chains, quinol: electron acceptor oxidoreductase, membrane protein
• Biological source: Chloroflexus aurantiacus J-10-fl; More
• Total number of polymer chains: 8
• Total formula weight: 303842.59

Authors

Xu, X.,Wu, W. (deposition date: 2024-07-01, release date: 2025-03-19)

Primary citation

Wu, W.,Fang, H.,He, H.,Wu, J.,Gong, Z.,Li, C.,Pei, X.,Xu, X.
Crystal structure of the alternative complex III from the phototrophic bacterium Chloroflexus aurantiacus.
Structure, 33:29-38.e2, 2025

PubMed Abstract: Alternative complex III (ACIII) is a multi-subunit quinol:electron acceptor oxidoreductase that couples quinol oxidation with transmembrane proton translocation in bacterial respiratory and photosynthetic electron transport chains. Four ACIII cryoelectron microscopy (cryo-EM) structures are known. However, the effects of cryo-EM versus X-ray crystallography structure determination on ACIII structure are unclear. Here, we report a 3.25 Å crystal structure of photosynthetic ACIII from Chloroflexus aurantiacus (CaACIIIp), revealing eight subunits (ActA-G and I) with four iron-sulfur clusters and six c-type hemes, a menaquinol-binding site, and two proton translocation passages. Structural comparisons with the previously reported cryo-EM structures reveal slight local conformational changes in the solvent-exposed regions of ActB, ActD, ActG, and the transmembrane (TM) helix of subunit I. The regions conferring structural flexibility possess low sequence conservation across species. However, the core functional modules containing the menaquinol-binding pocket, redox centers, and proton translocation passages remain unchanged, preserving the enzyme's activity.

PubMed: 39500318
DOI: 10.1016/j.str.2024.10.014

Experimental method

X-RAY DIFFRACTION (3.25 Å)