Lipid-Induced Conformational Changes within the Cytochrome b₆f Complex of Oxygenic Photosynthesis

Abstract

Cytochrome b6f catalyzes quinone redox reactions within photosynthetic membranes to generate a transmembrane proton electrochemical gradient for ATP synthesis. A key step involves electron transfer from the [2Fe-2S] cluster of the iron-sulfur protein (ISP) extrinsic domain to the cytochrome f heme across a distance of 26 Å, which is too large for competent electron transfer, but which could be bridged by translation-rotation of the ISP. Here we report the first crystallographic evidence for significant motion of the ISP extrinsic domain. It is inferred that extensive crystallographic disorder of the ISP extrinsic domain indicates conformational flexibility. The ISP disorder observed in the present structure, in contrast to the largely ordered ISP structure observed in the b6f complex supplemented with neutral lipids, is attributed to electrostatic interactions arising from anionic lipids.

Activation of the Stt7/STN7 Kinase through Dynamic Interactions with the Cytochrome b6f Complex

“…A specific role of the chlorophyll-binding niche in transmembrane signaling was suggested by the observation that insertion of an a-helix proximal to the chlorophyll-binding site inhibits state transitions (Zito et al, 2002). Based on site-directed mutagenesis of the chlorophyll a binding site, it was proposed that chlorophyll may play a role in the activation of the Stt7/STN7 kinase (de Lacroix de Lavalette et al, 2008;Hasan et al, 2013). It was further proposed that several lipid sites on the surface of Cytb 6 f complex close to the chlorophyll could form an adaptable surface for interaction with Stt7/STN7 kinase through lipid-mediated contacts .…”

Rieske Iron-Sulfur Protein Movement and Conformational Changes in Cytochrome bc–bf Complexes

“…Specifically, the Fe 2 atom of the cluster in the structures with an empty Q P site is 3.5-4.0 Å from its position in 4H13 (with TDS). There are no structures as yet illustrating the position in which the b 6 f ISP transfers an electron to cytochrome f. However a recent structure (4i7z) of the cyanobacterial complex treated with anionic phospholipids has a disordered ISP-ED, which is interpreted as meaning that it is fully released from cytochrome b and distributed over a large number of distal positions with low occupancy in any one position (Hasan et al 2013).…”

Inducible Repression of Nuclear-Encoded Subunits of the Cytochrome b6f Complex in Tobacco Reveals an Extraordinarily Long Lifetime of the Complex

“…Its active form is a dimer composed of eight different subunits with a total molecular mass of about 220 kD (Cramer et al, 2006;Baniulis et al, 2008). High-resolution structures of the cyt-bf have been obtained in the filamentous thermophilic cyanobacterium Mastigocladus laminosus (Kurisu et al, 2003;Hasan et al, 2013), in Nostoc sp. PCC 7120 (Baniulis et al, 2009), and in the unicellular eukaryotic alga Chlamydomonas reinhardtii (Stroebel et al, 2003).…”