X-ray structure of the dimeric cytochrome bc₁ complex from the soil bacterium Paracoccus denitrificans at 2.7-? resolution

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• 作者：Thomas  ; Kleinschroth^a ;   ; ^b ;   ; ^{thomas.kleinschroth@biochemie.uni-freiburg.de} ; Michela  ; Castellani^b ; Chi H.  ; Trinh^c ; Nina  ; Morgner^d ; Bernhard  ; Brutschy^d ; Bernd  ; Ludwig^b ; Carola  ; Hunte^a ;   ; ^{carola.hunte@biochemie.uni-freiburg.de}
• 关键词：Respiratory complex III ; Rhodobacteraceae ; Stigmatellin ; LILBID ; Membrane protein structure
• 刊名：Biochimica et Biophysica Acta (BBA)/Bioenergetics
• 出版年：2011
• 出版时间：December 2011
• 年：2011
• 卷：1807
• 期：12
• 页码：1606-1615
• 全文大小：2695 K

文摘

The respiratory cytochrome bc₁ complex is a fundamental enzyme in biological energy conversion. It couples electron transfer from ubiquinol to cytochrome c with generation of proton motive force which fuels ATP synthesis. The complex from the ¦Á-proteobacterium Paracoccus denitrificans, a model for the medically relevant mitochondrial complexes, lacked structural characterization. We show by LILBID mass spectrometry that truncation of the organism-specific, acidic N-terminus of cytochrome c₁ changes the oligomerization state of the enzyme to a dimer. The fully functional complex was crystallized and the X-ray structure determined at 2.7-? resolution. It has high structural homology to mitochondrial complexes and to the Rhodobacter sphaeroides complex especially for subunits cytochrome b and ISP. Species-specific binding of the inhibitor stigmatellin is noteworthy. Interestingly, cytochrome c₁ shows structural differences to the mitochondrial and even between the two Rhodobacteraceae complexes. The structural diversity in the cytochrome c₁ surface facing the ISP domain indicates low structural constraints on that surface for formation of a productive electron transfer complex. A similar position of the acidic N-terminal domains of cytochrome c₁ and yeast subunit QCR6p is suggested in support of a similar function. A model of the electron transfer complex with membrane-anchored cytochrome c₅₅₂, the natural substrate, shows that it can adopt the same orientation as the soluble substrate in the yeast complex. The full structural integrity of the P. denitrificans variant underpins previous mechanistic studies on intermonomer electron transfer and paves the way for using this model system to address open questions of structure/function relationships and inhibitor binding.