Structure of a Homodimeric Reaction Center and Insight Into the Evolution of Photosynthesis

Structure of a Homodimeric Reaction Center and Insight Into the Evolution of Photosynthesis

September 27, 2017

Address

727 E. Tyler St.
Tempe, AZ 85287

Location

Biodesign Institute, Auditorium

Date and Time

October 12, 2017, 4:00 pm (Length: 1 hour 0 minutes)

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Chris Gisriel, Graduate Researcher, School of Molecular Sciences, Arizona State University 

Reaction centers are pigment-protein complexes that drive photosynthesis by converting light into chemical energy. It is believed that they arose once from a homodimeric protein. The symmetry of a homodimer is broken in heterodimeric reaction-center structures, such as those reported previously. The 2.2-Å resolution X-ray structure of the homodimeric reaction center from the phototroph Heliobacterium modesticaldum exhibits C2 symmetry about a central axis. The core polypeptide dimer and two small subunits coordinate 54 bacteriochlorophylls and 2 carotenoids that capture and transfer energy to the electron transfer chain at the center, which performs charge separation and consists of 6 (bacterio)chlorophylls and an iron-sulfur cluster; unlike other reaction centers, it lacks a bound quinone. The comparison of this structure with those of other reaction centers has allowed us to make hypotheses about how photosynthesis evolved over billions of years.