A combined genetic, biochemical, and biophysical analysis of the phylloquinones in Photosystem I from a green algo

A combined genetic, biochemical, and biophysical analysis of the phylloquinones in Photosystem I from a green algo A combined genetic, biochemical, and biophysical analysis of the phylloquinones in Photosystem I from a green algo Phylloquinone (PhQ) serves as the secondary electron acceptor in photosystem I (PS1). It represents the transition from the organic chlorophyll cofactors to the inorganic ironsulfur clusters and from the time scale of picoseconds (PhQ reduction) to nanoseconds (PhQ reoxidation). The PS1 reaction center (RC) possesses two potential pathways for electron transfer between the primary electron donor, P700 and the FX iron-sulfur cluster. Each pathway consists of two chlorophylls and a PhQ. These cofactors are bound by the related PsaA and PsaB polypeptides, whose strongly conserved structural arrangement produces the striking symmetry of the reaction center structure. However, these two polypeptides are not identical, and their differences give rise to functional asymmetry within the A and B branches. Our previous study provided evidence that both PhQA and PhQB may be used in electron transfer (ET). Here we propose to continue our combined genetic and spectroscopic analysis, taking advantage of available structural data, improved instrumentation, and computational chemistry in order to understand how the polypeptide environment of PS1 contributes to the properties of the PhQ cofactors.