Nano-mechanical mapping of the interactions between surface-bound RC-LH1-PUFX core complexes and cytochrome [c.sub.2] attached to an AFM probe

• Published in: Photosynthesis research 2014-05, Vol.120 (1-2), p.169
• Main Authors: Vasilev, Cvetelin, Brindley, Amanda A, Olsen, John D, Saer, Rafael G, Beatty, J.T, Hunter, C.N
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Electron transport; Investigations; Photosynthesis; Phytochemistry; Proteins
• ISSN: 0166-8595; 1573-5079
• DOI: 10.1007/s11120-013-9812-7

Electron transfer pathways in photosynthesis involve interactions between membrane-bound complexes such as reaction centres with an extrinsic partner. In this study, the biological specificity of electron transfer between the reaction centre-light-harvesting 1-PufX complex and its extrinsic electron donor, cytochrome [c.sub.2], formed the basis for mapping the location of surface-attached RC-LH1-PufX complexes using atomic force microscopy (AFM). This nano-mechanical mapping method used an AFM probe functionalised with cyt [c.sub.2] molecules to quantify the interaction forces involved, at the single-molecule level under native conditions. With surface-bound RC-[His.sub.12]-LH1-PufX complexes in the photo-oxidised state, the mean interaction force with cyt [c.sub.2] is approximately 480 pN with an interaction frequency of around 66 %. The latter value lowered 5.5-fold when chemically reduced RC-[His.sub.12]-LH1-PufX complexes are imaged in the dark to abolish electron transfer from cyt [c.sub.2] to the RC. The correspondence between topographic and adhesion images recorded over the same area of the sample shows that affinity-based AFM methods are a useful tool when topology alone is insufficient for spatially locating proteins at the surface of photosynthetic membranes.