Mutational Studies on Conserved Histidine Residues in the Chlorophyll‐Binding Protein CP43 of Photosystem II

Abstract

Two chlorophyll-binding antenna proteins in the photosystem I1 core, CP43 and CP47, are structurally similar and are thought to have evolved from a common ancestor. Several conserved histidine residues in hydrophobic regions of CP47 have been shown to be important for photosystem I1 structure, function, and energy transfer. The purpose of this study was to determine whether similarly located histidine residues in CP43 function in a similar way. Three conserved histidine residues in presumed membranespanning regions of CP43, His40, HislO.5, and Hisll9, were mutated to glutamine (Q) and tyrosine (Y). The strains H105Q, H119Q, and H119Y were photoautotrophs whereas H40Q, H40Y, and H105Y were obligate photoheterotrophs. The H40Y and H105Y strains lacked detectable amounts of photosystem I1 reaction centers and hence could not evolve oxygen whereas H40Q retained a significant amount of photosystem I1 and oxygen evolution capacity. The observation that mutation of histidine residues to tyrosine has more drastic effects than mutation of these residues to glutamine is in agreement with results obtained for CP47 and suggests the involvement of these residues in chlorophyll binding. The drastic functional changes observed upon mutating His40 and His105 of CP43 are similar to those observed when mutating the corresponding histidine residues in CP47, thus suggesting that the similarity between CP43 and CP47 extends to the relative importance of functionally relevant residues. Interestingly, the His40+Gln mutation in CP43 had significant effects on photosystem I1 electron transfer in that it affected the thermodynamics of Qi oxidation by QB and increased the charge recombination rate between Q i and donor side components. This indicates that relatively minor changes in CP43 can significantly impact the properties of the photosystem I1 reaction center. The implications of this finding are discussed.Keywords: thylakoid ; photosynthesis ; photosystem 11; cyanobacteria; chlorophyll-binding protein Photosystem I1 (PS 11 A possibly significant difference between the CP47 and CP43 polypeptides is that CP43 can be removed easily from the , 3-(3,4-dichlorophenyi)-l ,I-dimethylurea; LHC 11: light-harvesting complex 11; PS, photosystem. PS I1 core either by mild chaotropic agents such as potassium thiocyanate [8] or by additional detergent treatment [9, 101 indicating a relatively loose association with PS 11. However, under these conditions the CP47 protein remains associated with the D1, D2, and cytochrome b,,, complex, suggesting that CP47 is closer to the PS I1 reaction center than CP43. This is in agreement with the conclusion drawn from comparisons of electron micrographs of isolated PS I1 reaction centers with and without CP43 11 11.Nonetheless, CP43 appears to be important for various as- short deletions in the long lumenal hydrophilic loop between membrane spanning helices V and VI showed that the integrity of this loop is an important factor for oxygen evolution and PS I1 stability [15]. In addition, introduction of parts of...

Photoassembly of the manganese cluster and oxygen evolution from monomeric and dimeric CP47 reaction center photosystem II complexes

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Investigating the Early Stages of Photosystem II Assembly in Synechocystis sp. PCC 6803

“…Previous work has shown that the availability of Chl a is important for the synthesis and accumulation of full-length CP47 apopolypeptide (33,34) and that absence of carotenoid leads to impaired synthesis of CP47 and especially of CP43 (35). Also, accumulation of CP47 and CP43 is severely impaired in site-directed mutants lacking an appropriate amino acid ligand to chlorophyll (36,37). These data therefore suggest that binding of pigment starts to occur at an early stage in the assembly of CP47 and CP43 in the WT, perhaps even cotranslationally during insertion of the apopolypeptides into the membrane to help stabilize the complex.…”

The Antenna System of Photosystem II From Thermosynechococcus elongatus at 3.2 Å Resolution

“…PsbC His119 in Synechocystis sp. PCC 6803 corresponding to His117 in T. elongatus; Manna and Vermaas 1997).…”