Sublocalization of Cytochrome b6f Complexes in Photosynthetic Membranes

It is well established that the majority of energy-converting photosynthetic protein complexes in plant thylakoid membrane are nonhomogenously distributed between stacked and unstacked membrane regions. Yet, the sublocalization of the central cytochrome b(6)f complex remains controversial. We present a structural model that explains the variation in cytochrome b(6)f sublocalization data. Small changes in the distance between adjacent membranes in stacked grana regions either allow or restrict access of cytochrome b(6)f complexes to grana. If the width of the gap falls below a certain threshold, then the steric hindrance prevents cytochrome b(6)f access to grana. Evidence is presented that the width of stromal gap is variable, demonstrating that the postulated mechanism can regulate the lateral distribution of the cytochrome b(6)f complexes.