Nano-mechanical mapping of the interactions between surface-bound RC-LH1-PufX core complexes and cytochrome c (2) attached to an AFM probe

摘要

Electron transfer pathways in photosynthesisudinvolve interactions between membrane-bound complexesudsuch as reaction centres with an extrinsic partner. In thisudstudy, the biological specificity of electron transfer betweenudthe reaction centre-light-harvesting 1-PufX complex and itsudextrinsic electron donor, cytochrome c2, formed the basisudfor mapping the location of surface-attached RC-LH1-PufXudcomplexes using atomic force microscopy (AFM). Thisudnano-mechanical mapping method used an AFM probeudfunctionalised with cyt c2 molecules to quantify the interactionudforces involved, at the single-molecule level underudnative conditions. With surface-bound RC-His12-LH1-PufXudcomplexes in the photo-oxidised state, the mean interactionudforce with cyt c2 is approximately 480 pN with an interactionudfrequency of around 66 %. The latter value loweredud5.5-fold when chemically reduced RC-His12-LH1-PufXudcomplexes are imaged in the dark to abolish electronudtransfer from cyt c2 to the RC. The correspondence betweenudtopographic and adhesion images recorded over the sameudarea of the sample shows that affinity-based AFM methodsudare a useful tool when topology alone is insufficient forudspatially locating proteins at the surface of photosyntheticudmembranes.