Mutation of a single residue, β-glutamate-20, alters protein–lipid interactions of light harvesting complex II

It is well established that assembly of the peripheral antenna complex, LH2, is required for proper photosynthetic membrane biogenesis in the purple bacterium Rhodobacter sphaeroides. The underlying interactions are, as yet, not understood. Here we examined the relationship between the morphology of the photosynthetic membrane and the lipid–protein interactions at the LH2–lipid interface. The non-bilayer lipid, phosphatidylethanolamine, is shown to be highly enriched in the boundary lipid phase of LH2. Sequence alignments indicate a putative lipid binding site, which includes β-glutamate-20 and the adjacent carotenoid end group. Replacement of β-glutamate-20 with alanine results in significant reduction of phosphatidylethanolamine and concomitant raise in phosphatidylcholine in the boundary lipid phase of LH2 without altering the lipid composition of the bulk phase. The morphology of the LH2 housing membrane is, however, unaffected by the amino acid replacement. In contrast, simultaneous modification of glutamate-20 and exchange of the carotenoid sphaeroidenone with neurosporene results in significant enlargement of the vesicular membrane invaginations. These findings suggest that the LH2 complex, specifically β-glutamate-20 and the carotenoids' polar head group, contribute to the shaping of the photosynthetic membrane by specific interactions with surrounding lipid molecules

Superoxide destroys the [2Fe-2S]2+ cluster of FNR from Escherichia coli

Sutton VR, Stubna A, Patschkowski T, Munck E, Beinert H, Kiley PJ. Superoxide destroys the [2Fe-2S]2+ cluster of FNR from Escherichia coli. Biochemistry. 2004;43(3):791-798.The oxygen sensing ability of the transcription factor FNR depends on the presence of a [4Fe-4S]2+ cluster. In the presence of O2, conversion of the [4Fe-4S]2+ cluster to a [2Fe-2S]2+ cluster inactivates FNR, but the fate of the [2Fe-2S]2+ cluster in cells grown under aerobic conditions is unknown. The present study shows that the predominant form of FNR in aerobic cells is apo-FNR (cluster-less FNR) indicating that the [2Fe-2S]2+ cluster, like the [4Fe-4S]2+ cluster, is not stable under these conditions. By quantifying the amount of [2Fe-2S]2+ cluster in 2Fe-FNR in vitro in the presence of various reductants and oxidants (GSH, DTT, cysteine, O2, hydrogen peroxide, and superoxide), we found that superoxide, a byproduct of aerobic metabolism, significantly destabilized the [2Fe-2S]2+ cluster. Mössbauer spectroscopy was used to monitor the effects of superoxide on 2Fe-FNR in vivo; under cellular conditions that favored superoxide production, we observed the disappearance of the signal representative of the [2Fe-2S]2+ cluster. We conclude that the [2Fe-2S]2+ cluster of FNR is labile to superoxide both in vitro and in vivo. This lability may explain the absence of the [2Fe-2S]2+ cluster form of FNR under aerobic growth conditions