Structural and functional characterisation of the cyanobacterial PetC3 Rieske protein family

Abstract

The cyanobacterium Synechocystis PCC 6803 possesses three Rieske isoforms: PetC1, PetC2 and PetC3. While PetC1 and PetC2 have been identified as alternative subunits of the cytochrome bf complex (bf), PetC3 was localized exclusively within the plasma membrane. The spatial separation of PetC3 from the photosynthetic and respiratory protein complexes raises doubt in its involvement in bioenergetic electron transfer. Here we report a detailed structural and functional characterization of the cyanobacterial PetC3 protein family indicating that PetC3 is not a component of the bf and the photosynthetic electron transport as implied by gene annotation. Instead PetC3 has a distinct function in cell envelope homeostasis. Especially proteomic analysis shows that deletion of petC3 in Synechocystis PCC 6803 primarily affects cell envelope proteins including many nutrient transport systems. Therefore, the observed downregulation in the photosynthetic electron transport - mainly caused by photosystem 2 inactivation - might constitute a stress adaptation. Comprehensive in silico sequence analyses revealed that PetC3 proteins are periplasmic lipoproteins tethered to the plasma membrane with a subclass consisting of soluble periplasmic proteins, i.e. their N-terminal domain is inconsistent with their integration into the bf. For the first time, the structure of PetC3 was determined by X-ray crystallography at an atomic resolution revealing significant high similarities to non-bf Rieske subunits in contrast to PetC1. These results suggest that PetC3 affects processes in the periplasmic compartment that only indirectly influence photosynthetic electron transport. For this reason, we suggest to rename "Photosynthetic electron transport Chain 3" (PetC3) proteins as "periplasmic Rieske proteins" (Prp).

The structure of the complex between the arsenite oxidase from Pseudorhizobium banfieldiae sp. strain NT-26 and its native electron acceptor cytochrome c 552

“…3a, Supplementary Table S2). This suggests a role for Pro122 in the electron transfer process, which is consistent with its conservation in the sequences of Rieske cluster-containing proteins and subunits, including arsenite oxidase from Alcaligenes faecalis (PDB entry 1g8k; Ellis et al, 2001), the Rieske protein II SoxF from Sulfolobus acidocaldarius (Sf SoxF; PDB entry 1jm1; Bo ¨nisch et al, 2002), the Rieske protein from Thermus thermophilus (TtRp; PDB entry 1nyk; Hunsicker-Wang et al, 2003) and the Rieske protein involved in photosynthetic and respiratory electron transport in Synechocystis PCC 6803 (SyPetC3; PDB entry 5cxm; Veit et al, 2016;Fig. 3b).…”

Soluble domains of cytochrome c-556 and Rieske iron–sulfur protein from Chlorobaculum tepidum: Crystal structures and interaction analysis

“…The structure of the Rieske sol protein can be divided into two subdomains ( Bönisch et al, 2002 ; Veit et al, 2016 ). One is a small cluster-binding subdomain that contains a [2Fe–2S] cluster constituted on a scaffold β-sheet 3 (β5–β7) along with ligand loops 1 and 2 and the proline loop (described below).…”

Absolute quantification of cellular levels of photosynthesis-related proteins in Synechocystis sp. PCC 6803

“…al 2008 ) or high light stress (Tsunoyama et al 2009 ) was undetectable. The third ISP, PetC3 (sll1182-encoded) was identified in our analyses (Supplementary Data Sets S1 and S2), however, it is localized to the cytoplasmic, not thylakoid membrane (Aldridge et al 2008 ) where its function appears unrelated to photosynthetic electron transport (Veit et al 2016a ).…”

“…The minimum and maximum cpc values are rounded to the nearest 10 (< 1000), 50 (1000-10,000) or 500 (> 10,000) and displayed as bars, shaded according to cpc range, for photosystem II (PSII, PsbA-H), photosystem I (PSI, PsaA-F) (a), cytochrome b 6 f (cytb 6 f), PetP, phycocyanin (PC), photosynthetic NAD(P)H dehydrogenase-like complex type-1 (NDH-1) (b) and ATP synthase (c). Abundance levels corresponding to the largest extent of overlap between subunits, shown by the horizontal dashed lines, are taken to represent probable ranges for the complexes, explained in Results and Discussion: PSII (24,000-44,000 cpc), PSI (86,000-118,500 cpc), cytb 6 f (3350-8450 or 14,000-28,000 cpc), NDH-1 (7000-13,500 cpc), ATP synthase (α, β: 67,000-83,500 cpc; γ, δ, ε, a, b, b': 12,000-25,000 cpc) 2008) where its function appears unrelated to photosynthetic electron transport (Veit et al 2016a).…”