TCBG Seminar

Dimerization affinity of a single transmembrane helix can determine the oligomerization state of a large multi-protein complex

Dr. Jen Hsin
Department of Bioengineering
Stanford University
Palo Alto, CA

Tuesday, February 21, 2012
3:00 pm (CT)
3169 Beckman Institute


Complex formation is often the critical step before proteins can fulfill their cellular functions. How multiple proteins are assembled into a specific organization is an important question in biochemistry and cell biology. In photosynthetic bacteria, the initial steps of photosynthesis are carried out in the large membrane protein assembly called the photosynthetic core complex. The core complex contains mainly the light-harvesting complex I (LH1) and the reaction center (RC), but in the Rhodobacter (Rba.) species, an additional transmembrane single-helix protein, PufX, is also found within the complex. PufX has been identified as the main determinant of the organization of Rba. core complex: while some species have monomeric, ring-shaped core complex, some produce dimeric, S- shaped core complex that become monomeric when PufX is deleted. To address how PufX of some Rba. species promote core complex dimerization, and some do not, we carried out a series of computational and biochemical assays measuring the dimerization affinity of different PufX helices. Both approaches demonstrated that the PufX helix from the species with monomeric core complexes had no detectable preference for dimerization, while all other PufX helices from species with dimeric core complexes showed some capability of dimerization. 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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