Preliminary X-ray crystallographic analysis of MntC, a periplasmic manganese binding component of a Mn transporter from Synechocystis sp. PCC 6803

Abstract

Photosystem II contains the site of photosynthetic electron transfer initiation, water oxidation and quinone reduction in higher plants, algae and cyanobacteria. This complex contains a reaction center (RCII), antenna proteins and additional proteins with accessory or regulatory roles. In order to elucidate the biochemical and biophysical characteristics of the entire system, it is necessary to obtain information on the three-dimensional structures of all of the protein constituents. Our laboratory is involved in the determination of the structure of a number of PSII components. 1) We have crystallized the RCII complex from higher plants (monomeric and dimeric forms). Monomeric oxygen-evolving RCII from higher plants was crystallized in nine different detergent mixtures. We have used a variety of methodologies to probe the interaction between these detergents and the RCII complex. Recent results with cyanobacteria will also be shown. 2) We have solved the structure of C-phycocyanin, a PSII phycobilisome antenna protein from Synechococcus vulcanus at 2.5Å (PDB code 1I7Y). We have identified structural characteristics leading to thermal stability in phycobilisomes, by comparisons with other phycocyanins of known structure. 3) We have obtained crystals diffracting to 3.2Å, and begun structure determination, of the MntC protein from Synechocystis sp. PCC 6803, which is one of the proteins required for uptake and transport of manganese ions needed in PSII. 4) We have obtained microcrystals of dimers of spinach OEC manganese stabilizing protein (33 kDa protein). We have studied the behavior of this protein in vitro, and the results have lead to proposals on the function of this protein in vivo.