The Type 1 Homodimeric Reaction Center in Heliobacterium modesticaldum

Project: Research project


Compared to Photosystem I, our understanding of homodimeric, Type I (Fe/S-cluster) reaction centers is primitive. The electron transfer cofactors are still being characterized, the protein composition is just coming into focus, the ability to make mutants is not yet possible, and there are few, if any, structural details available. This lack of progress is due partly to the fact that heliobacteria and green sulfur bacteria are strict anaerobes, with all of the attendant problems of growing the organisms and purifying the components in an oxygen-free environment. In the case of the heliobacterial reaction center (HbRC), the oxygen sensitivity is exacerbated by rapid destruction of the FA/FB clusters and the facile conversion of the BChl g pigments to a Chl a-like molecule. In this proposal, two experienced photosynthesis researchers, Kevin Redding (Arizona State University) and John Golbeck (Penn State University) propose to continue their collaborative research program aimed at understanding the process of charge separation and stabilization in the Type I homodimeric reaction center in Heliobacterium modesticaldum. What we know from the current funding period is that (i) a reaction center core consisting of the (PshA)2 homodimer can be purified to homogeniety; (ii) the FA and FB clusters are located on two loosely-bound proteins, PshB1 and PshB2; (iii) the genes for these proteins, HM1-1461 and HM1-1462 form an operon from which a single message is transcribed; (iv) the FX cluster is present in a ground spin state of S = 3/2 and has a surprisingly high reduction potential; (v) the HbRC core lacking PshB polypeptides can photo-reduce several different electron acceptors; (v) the enigmatic fluorescence emission from whole heliobacterial cells correlates with charge recombination between A0 and P800+, and (vi) the partial conversion of Bchl g to Chl aF is accompanied by a change in the CIDNP spectrum that is best explained if the intermediate accessory pigment, rather than the primary donor (P8
Effective start/end date9/1/138/31/19


  • DOE: Chicago Service Center: $1,694,500.00


Photosystem I Protein Complex
Chemical analysis