Abstract
Photosystem (PS) I is a large membrane protein complex vital for oxygenic photosynthesis, one of the most important biological processes on the planet. We present an "atomic" model of higher plant PSI, based on theoretical modeling using the recent 4.4 angstroms x-ray crystal structure of PSI from pea. Because of the lack of information on the amino acid side chains in the x-ray structural model and the high cofactor content in this system, novel modeling techniques were developed. Our model reveals some important structural features of plant PSI that were not visible in the crystal structure, and our model sheds light on the evolutionary relationship between plant and cyanobacterial PSI.
Highlights
For chemically similar compounds [19]
The conformation we suggest is partially supported by the electron density map from the plant PSI crystal structure and is the most probable conformation
The model presented here shows for the first time details of the unique structural and functional features of plant PSI
Summary
Four external light-harvesting complexes, tentatively assigned to Lhca, Lhca, Lhca, and Lhca. In most of the conserved subunits, the protein backbone conformation is virtually identical (see TABLE ONE). Because a 4.4 Å structure is able to reveal the location of the protein backbone but not the identity or conformation of the amino acid side chains, the plant PSI crystal structure answers many questions but allows us to ask many more. If the backbone conformation is so similar, what accounts for the functional differences between plant and cyanobacterial PSI? To answer some of these questions and to provide detailed information for mutagenesis experiments and functional studies, we have derived an atomic level computational model of plant photosystem I (Protein Data Bank code 1YO9). LHCII belongs to the same protein family as LHCI and is helpful in the modeling of the LHCI proteins
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