TCB Publications - Abstract
Jen Hsin, Loren LaPointe, Alla Kazy, Christophe Chipot, Alessandro Senes, and Klaus Schulten. Oligomerization state of photosynthetic core complexes is correlated with the dimerization affinity of a transmembrane helix. Journal of the American Chemical Society, 133:14071-14081, 2011. (PMC: 3168531)
-helix, PufX, is found within the core complex, an essential photosynthetic
macromolecular assembly that performs the absorption and the initial processing of light
energy. Despite its structural simplicity, many unresolved questions surround PufX, the
most important of which is its location within the photosynthetic core complex. One
proposed placement of PufX is at the center of a core complex dimer, where two PufX
helices associate in the membrane and form a homodimer. Inability for PufX of certain Rba.
species to form a homodimer is thought to lead to monomeric core complexes. In the
present study, we employ a combination of computational and experimental techniques to
test the hypothesized homodimerization of PufX. We carry out a systematic investigation to
measure the dimerization affinity of PufX from four Rba. species, using a molecular
dynamics-based free-energy method, as well as experimental TOXCAT assays. We found
that the four PufX helices have substantially different dimerization affinities. Both
computational and experimental techniques demonstrate that species with dimeric core
complexes have PufX that can potentially form a homodimer, whereas the one species with
monomeric core complexes has a PufX with little to no dimerization propensity. Our
analysis of the helix-helix interface revealed a number of positions that may be important
for PufX dimerization and the formation of a hydrogen bond network between these GxxxG
containing helices. Our results suggest that the different oligomerization states of core
complexes in various Rba. species can be attributed, among other factors, to the different
propensity of its PufX helix to homodimerize.
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