TY - JOUR
T1 - No evidence from FTIR difference spectroscopy that aspartate-342 of the D1 polypeptide ligates a Mn ion that undergoes oxidation during the S0 to S1, S1 to S2, or S2 to S 3 transitions in photosystem II
AU - Strickler, Melodie A.
AU - Walker, Lee M.
AU - Hillier, Warwick
AU - Britt, R. David
AU - Debus, Richard J.
PY - 2007/3/20
Y1 - 2007/3/20
N2 - In the recent X-ray crystallographic structural models of photosystem II, Asp342 of the D1 polypeptide is assigned as a ligand of the oxygen-evolving Mn4 cluster. To determine if D1-Asp342 ligates a Mn ion that undergoes oxidation during one or more of the S0 → S 1, S1 → S2, and S2 → S3 transitions, the FTIR difference spectra of the individual S state transitions in D1-D342N mutant PSII particles from the cyanobacterium Synechocystis sp. PCC 6803 were compared with those in wild-type PSII particles. Remarkably, the data show that the mid-frequency (1800-1200 cm-1) FTIR difference spectra of wild-type and D1-D342N PSII particles are essentially identical. Importantly, the mutation alters none of the carboxylate vibrational modes that are present in the wild-type spectra. The absence of significant mutation-induced spectral alterations in D1-D342N PSII particles shows that the oxidation of the Mn4 cluster does not alter the frequencies of the carboxylate stretching modes of D1-Asp342 during the S0 → S 1, S1 → S2, or S2 → S 3 transitions. One explanation of these data is that D1-Asp342 ligates a Mn ion that does not increase its charge or oxidation state during any of these S state transitions. However, because the same conclusion was reached previously for D1-Asp170, and because the recent X-ray crystallographic structural models assign D1-Asp170 and D1-Asp342 as ligating different Mn ions, this explanation requires that (1) the extra positive charge that develops on the Mn4 cluster during the S1 → S2 transition be localized on the Mn ion that is ligated by the α-COO - group of D1-Ala344 and (2) any increase in positive charge that develops on the Mn4 cluster during the S0 → S 1 and S2 → S3 transitions be localized on the one Mn ion that is not ligated by D1-Asp170, D1-Asp342, or D1-Ala344. In separate experiments that were conducted with L-[1-13C]alanine, we found no evidence that D1-Asp342 ligates the same Mn ion that is ligated by the α-COO- group of D1-Ala344.
AB - In the recent X-ray crystallographic structural models of photosystem II, Asp342 of the D1 polypeptide is assigned as a ligand of the oxygen-evolving Mn4 cluster. To determine if D1-Asp342 ligates a Mn ion that undergoes oxidation during one or more of the S0 → S 1, S1 → S2, and S2 → S3 transitions, the FTIR difference spectra of the individual S state transitions in D1-D342N mutant PSII particles from the cyanobacterium Synechocystis sp. PCC 6803 were compared with those in wild-type PSII particles. Remarkably, the data show that the mid-frequency (1800-1200 cm-1) FTIR difference spectra of wild-type and D1-D342N PSII particles are essentially identical. Importantly, the mutation alters none of the carboxylate vibrational modes that are present in the wild-type spectra. The absence of significant mutation-induced spectral alterations in D1-D342N PSII particles shows that the oxidation of the Mn4 cluster does not alter the frequencies of the carboxylate stretching modes of D1-Asp342 during the S0 → S 1, S1 → S2, or S2 → S 3 transitions. One explanation of these data is that D1-Asp342 ligates a Mn ion that does not increase its charge or oxidation state during any of these S state transitions. However, because the same conclusion was reached previously for D1-Asp170, and because the recent X-ray crystallographic structural models assign D1-Asp170 and D1-Asp342 as ligating different Mn ions, this explanation requires that (1) the extra positive charge that develops on the Mn4 cluster during the S1 → S2 transition be localized on the Mn ion that is ligated by the α-COO - group of D1-Ala344 and (2) any increase in positive charge that develops on the Mn4 cluster during the S0 → S 1 and S2 → S3 transitions be localized on the one Mn ion that is not ligated by D1-Asp170, D1-Asp342, or D1-Ala344. In separate experiments that were conducted with L-[1-13C]alanine, we found no evidence that D1-Asp342 ligates the same Mn ion that is ligated by the α-COO- group of D1-Ala344.
UR - http://www.scopus.com/inward/record.url?scp=33947380152&partnerID=8YFLogxK
U2 - 10.1021/bi062195e
DO - 10.1021/bi062195e
M3 - Article
SN - 0006-2960
VL - 46
SP - 3151
EP - 3160
JO - Biochemistry
JF - Biochemistry
IS - 11
ER -