Structure of redox components in Photosystem 2 studied with computer modelling, site-dírected mutagenesís and EPR spectroscopy

Title:

Structure of redox components in Photosystem 2 studied with computer modelling, site-dírected mutagenesís and EPR spectroscopy

Creator:

Styring, S., Davidsson, L., Tommos, C., Vermaas, W., Vass, I., and Svensson, B.

Identifier:

https://cdk.lib.cas.cz/client/handle/uuid:fd473bc0-57d3-44a8-a013-118ab110c346
uuid:fd473bc0-57d3-44a8-a013-118ab110c346
urnnbn:urn:nbn:cz:aba007-000fds

Type:

model:internalpart and TEXT

Format:

print

Description:

The oxidizing side of photosystem 2 (PS2) contains a set of unique redox components including two tyrosine radicals, Tyr2 and Tyrp, and a cluster of 4 Mn atoms that are involved in the oxidation of water to molecular oxygen. The structural environment of these components is unknown; we ušed computer-assisted modelling to create a three-dimensional model for the structure around Tyr^ and Tyrj). The tyrosines are predicted to be located in hydrophobic cavities in the Dl and D2 reaction centre proteins, respectively. The cavities are situated close to the lumenal surface of the thylakoid membrane and are surrounded mainly by highly conserved amino acid residues. Both tyrosines are proposed to be hydrogen-bonded to the nearby histidine residues Hisl90 on respective protein. We tested the model by electron paramagnetic resonance (EPR) spectroscopy of Tyr^ and site-directed mutagenesis of the D2 protein in the cyanobacterium Synechocystis 6803. In two mutants, where the corresponding histidine is changed to a tyrosine or a leucine, the normál EPR spectra from Tyr^ were drastically altered to narrow structureless radical signals with g-values similar to that of Tyrp (g » 2.0050). The new spectra were assigned to Tyrp from functional experiments and the spectral modification indicated that the introduced point-mutation of His 190 (D2-Hisl89 in Synechocystis 6803) modified the environment around Tyr^ supporting the structural model. In a third mutant where Glnl65 (D2-Glnl64 in Synechocystis 6803) was exchanged to a leucine we also observed a modified EPR spectrum consistent with the predictions firom the model. AU the experimental data obtained strengthen the Computer derived model in essential aspects. We also predicted a possible location for the Mn-cluster to the loop that connects the membrane spanning helices A and B on the Dl protein. In addition the structural model suggests the presence of a metal-site, possibly a Mn site, close to Tyrz on the Dl protein. The site is proposed to be constituted of three residues on the Dl protein, Glnl65, Aspl70 and Glul89.

Language:

Multiple languages

Rights:

http://creativecommons.org/licenses/by-nc-sa/4.0/
policy:public

Coverage:

225-241 and 67-83

Source:

Photosynthetica | 1993 Volume:28 | Number:2

Harvested from:

CDK

Metadata only:

false