PARENT SESSION
Posters P4Aa Chlorophyll and bilin based antenna systems. Abstracts (239-271)

All-atom model of plant Photosystem I. Craig Jolley^*,1, Adam Ben-Shem², Nathan Nelson², Petra Fromme¹, ¹ Arizona State University, U.S.A.² Tel Aviv University, Israel

ABSTRACT- Although an all-atom structure for plant photosystem I could provide valuable insight into the detailed function of this important membrane protein complex, no high-resolution structures of plant PSI have yet been published. A 2.5 structure of the trimeric cyanobacterial photosystem I provided the first view into the complex architecture of a closely related system, consisting of 12 different proteins to which 127 cofactors are non-covalently attached. The complex has a molecular mass of 1056 kDa, consisting of about 150,000 atoms. In addition to the core structure, which is conserved between cyanobacteria and higher plants, the latter contain peripheral antenna proteins, the light harvesting complex I (LHCI). Recently a supercomplex of plant photosystem I with its peripheral LHCI antenna has been crystallized and a low-resolution structure of this PSI-LHCI supercomplex from pivum sativum (garden pea) has been obtained by X-ray structure analysis at 4.4 resolution. The structure showed the main structural elements of the plant Photosystem I complex, however no structural details (e.g. amino acid side chains and structural details of the cofactors) had been determined, due to the limited resolution. Additional insight into the structure of the LHCI proteins can be obtained from a recent 2.72 structure of the plant LHCII complex, which is closely related. We are working toward an all-atom model of the plant PSI-LHCI supercomplex by fleshing out the low-resolution structure with homology modeling based on the high-resolution structure of these related systems. In order to obtain a reasonable model, a large variety of biochemical and biophysical data and sequence information obtained from plant Photosystem I, plant antenna complexes, and cyanobactieral photosystems has to be taken into account.

KEY WORDS: light-harvesting complex, photosystem I, homology modeling