Participation of Glutamate-333 of the D1 Polypeptide in the Ligation of the Mn4CaO5 Cluster in Photosystem II

作者：Service Rachel J; Yano Junko; Dilbeck Preston L; Burnap Robert L; Hillier Warwick; Debus Richard J^*

来源：Biochemistry, 2013, 52(47): 8452-8464.

DOI：10.1021/bi401339f

In the 1.9 angstrom structural model of photosystem II (PDB: 3ARC), the amino acid residue Glu333 of the D1 polypeptide coordinates to the oxygen-evolving Mn4CaO5 cluster. This residue appears to be highly significant in that it bridges the two Mn ions (Mn-B3 and the %26quot;dangling%26quot; Mn-A4) that are also bridged by the oxygen atom O-5. This oxygen atom has been proposed to be derived from one of two substrate water molecules and to become incorporated into the product dioxygen molecule during the final step in the catalytic cycle. In addition, the backbone nitrogen of D1-Glu333 interacts directly with a nearby Cl- atom. To further explore the influence of this structurally unique residue on the properties of the Mn4CaO5 cluster, the D1-E333Q mutant of the cyanobacterium Synechocystis sp. PCC 6803 was characterized with a variety of biophysical and spectroscopic methods, including polarography, EPR, X-ray absorption, and FTIR difference spectroscopy. The kinetics of oxygen release in the mutant were essentially unchanged from those in wild-type. In addition, the oxygen flash yields exhibited normal period-four oscillations having normal S state parameters, although the yields were lower, indicative of the mutant%26apos;s lower steady-state dioxygen evolution rate of approximately 30% compared to that of the wild-type. The S-1 state Mn-XANES and Mn-EXAFS and S-2 state multiline EPR signals of purified D1-E333Q PSII core complexes closely resembled those of wild-type, aside from having lower amplitudes. The Sn+1-minus-S-n FTIR difference spectra showed only minor alterations to the carbonyl, amide, and carboxylate stretching regions. However, the mutation eliminated a negative peak at 3663 cm(-1) in the weakly H-bonding O-H stretching region of the S-2-minus-S-1 FTIR difference spectrum and caused an approximately 9 cm(-1) downshift of the negative feature in this region of the S-1-minus-S-0 FTIR difference spectrum. We conclude that fully functional Mn4CaO5 clusters assemble in the presence of the D1-E333Q mutation but that the mutation decreases the yield of assembled clusters and alters the H-bonding properties of one or more water molecules or hydroxide groups that are located on or near the Mn4CaO5 cluster and that either deprotonate or form stronger hydrogen bonds during the S-0 to S-1 and S-1 to S-2 transitions.

• 出版日期2013-11-26