Deciphering protein-protein interactions during the biogenesis of cytochrome c oxidase from Paracoccus denitrificans

Diversity of Cytochrome c Oxidase Assembly Proteins in Bacteria

Cytochrome c oxidase in animals, plants and many aerobic bacteria functions as the terminal enzyme of the respiratory chain where it reduces molecular oxygen to form water in a reaction coupled to energy conservation. The three-subunit core of the enzyme is conserved, whereas several proteins identified to function in the biosynthesis of the common family A1 cytochrome c oxidase show diversity in bacteria. Using the model organisms Bacillus subtilis, Corynebacterium glutamicum, Paracoccus denitrificans, and Rhodobacter sphaeroides, the present review focuses on proteins for assembly of the heme a, heme a₃, Cu_B, and Cu_A metal centers. The known biosynthesis proteins are, in most cases, discovered through the analysis of mutants. All proteins directly involved in cytochrome c oxidase assembly have likely not been identified in any organism. Limitations in the use of mutants to identify and functionally analyze biosynthesis proteins are discussed in the review. Comparative biochemistry helps to determine the role of assembly factors. This information can, for example, explain the cause of some human mitochondrion-based diseases and be used to find targets for new antimicrobial drugs. It also provides information regarding the evolution of aerobic bacteria.

Identification of candidate genes from androgenic gland in Macrobrachium nipponense regulated by eyestalk ablation

The eyestalk of crustaceans, such as Macrobrachium nipponense, contains many neurosecretory hormones affecting the process of reproduction, molting, metabolism of glucose, and other functions. In this study, important metabolic pathways and candidate genes involved in male sexual development were selected from M. nipponense. The methodology involved performing long-read and next generation transcriptome sequencing of genes from the androgenic gland after eyestalk ablation. qPCR analysis revealed that the mRNA expression of Mn-IAG was significantly increased after ablation of both the single-side (SS) and double-side (DS) eyestalk, compared with the control group (CG). The long-read transcriptome generated 49,840 non-redundant transcripts. A total of 1319, 2092 and 4351 differentially expressed genes (DEGs) were identified between CG versus SS, SS versus DS and CG versus DS, respectively. These data indicated that ablation of the double-sided eyestalk played stronger regulatory roles than the single-side ablation on male sexual development in M. nipponense. This was consistent with the qPCR analysis. Cell Cycle, Cellular Senescence, Oxidative Phosphorylation, Glycolysis/Gluconeogenesis and Steroid Hormone Biosynthesis were the primary enriched metabolic pathways in all three comparisons, and the important genes from these metabolic pathways were also selected. qPCR permitted secondary confirmation of ten DEGs identified through RNA-seq. RNAi-mediated silencing analyses of Hydroxysteroid dehydrogenase like 1 (HSDL1) revealed that HSDL1 has a positive regulatory effect on testes development. This study provides valuable insight into male sexual development in M. nipponense, including metabolic pathways and genes, paving the way for advanced studies on male sexual development in this species and in other crustaceans.

Handling of nutrient copper in the bacterial envelope

The insertion of copper into bacterial cuproenzymesin vivodoes not always require a copper-binding metallochaperone – why?

Characterization and effect of metal ions on the formation of the Thermus thermophilus Sco mixed disulfide intermediate

The Sco protein from Thermus thermophilus has previously been shown to perform a disulfide bond reduction in the Cu_A protein from T. thermophilus, which is a soluble protein engineered from subunit II of cytochrome ba ₃ oxidase that lacks the transmembrane helix. The native cysteines on TtSco and TtCu_A were mutated to serine residues to probe the reactivities of the individual cysteines. Conjugation of TNB to the remaining cysteine in TtCu_A and subsequent release upon incubation with the complementary TtSco protein demonstrated the formation of the mixed disulfide intermediate. The cysteine of TtSco that attacks the disulfide bond in the target TtCu_A protein was determined to be TtSco Cysteine 49. This cysteine is likely more reactive than Cysteine 53 due to a higher degree of solvent exposure. Removal of the metal binding histidine, His 139, does not change MDI formation. However, altering the arginine adjacent to the reactive cysteine in Sco (Arginine 48) does alter the formation of the MDI. Binding of Cu²⁺ or Cu⁺ to TtSco prior to reaction with TtCu_A was found to preclude formation of the mixed disulfide intermediate. These results shed light on a mechanism of disulfide bond reduction by the TtSco protein and may point to a possible role of metal binding in regulating the activity. IMPORTANCE: The function of Sco is at the center of many studies. The disulfide bond reduction in Cu_A by Sco is investigated herein and the effect of metal ions on the ability to reduce and form a mixed disulfide intermediate are also probed.

Widespread Distribution and Functional Specificity of the Copper Importer CcoA: Distinct Cu Uptake Routes for Bacterial Cytochrome c Oxidases

Cytochrome c oxidases are members of the heme-copper oxidase superfamily. These enzymes have different subunits, cofactors, and primary electron acceptors, yet they all contain identical heme-copper (Cu_B) binuclear centers within their catalytic subunits. The uptake and delivery pathways of the Cu_B atom incorporated into this active site, where oxygen is reduced to water, are not well understood. Our previous work with the facultative phototrophic bacterium Rhodobacter capsulatus indicated that the copper atom needed for the Cu_B site of cbb₃-type cytochrome c oxidase (cbb₃-Cox) is imported to the cytoplasm by a major facilitator superfamily-type transporter, CcoA. In this study, a comparative genomic analysis of CcoA orthologs in alphaproteobacterial genomes showed that CcoA is widespread among organisms and frequently co-occurs with cytochrome c oxidases. To define the specificity of CcoA activity, we investigated its function in Rhodobacter sphaeroides, a close relative of R. capsulatus that contains both cbb₃- and aa₃-Cox. Phenotypic, genetic, and biochemical characterization of mutants lacking CcoA showed that in its absence, or even in the presence of its bypass suppressors, only the production of cbb₃-Cox and not that of aa₃-Cox was affected. We therefore concluded that CcoA is dedicated solely to cbb₃-Cox biogenesis, establishing that distinct copper uptake systems provide the Cu_B atoms to the catalytic sites of these two similar cytochrome c oxidases. These findings illustrate the large variety of strategies that organisms employ to ensure homeostasis and fine control of copper trafficking and delivery to the target cuproproteins under different physiological conditions.IMPORTANCE The cbb₃- and aa₃-type cytochrome c oxidases belong to the widespread heme-copper oxidase superfamily. They are membrane-integral cuproproteins that catalyze oxygen reduction to water under hypoxic and normoxic growth conditions. These enzymes diverge in terms of subunit and cofactor composition, yet they all share a conserved heme-copper binuclear site within their catalytic subunit. In this study, we show that the copper atoms of the catalytic center of two similar cytochrome c oxidases from this superfamily are provided by different copper uptake systems during their biogenesis. This finding illustrates different strategies by which organisms fine-tune the trafficking of copper, which is an essential but toxic micronutrient.

Cytochrome c Oxidase Biogenesis and Metallochaperone Interactions: Steps in the Assembly Pathway of a Bacterial Complex

Biogenesis of mitochondrial cytochrome c oxidase (COX) is a complex process involving the coordinate expression and assembly of numerous subunits (SU) of dual genetic origin. Moreover, several auxiliary factors are required to recruit and insert the redox-active metal compounds, which in most cases are buried in their protein scaffold deep inside the membrane. Here we used a combination of gel electrophoresis and pull-down assay techniques in conjunction with immunostaining as well as complexome profiling to identify and analyze the composition of assembly intermediates in solubilized membranes of the bacterium Paracoccus denitrificans. Our results show that the central SUI passes through at least three intermediate complexes with distinct subunit and cofactor composition before formation of the holoenzyme and its subsequent integration into supercomplexes. We propose a model for COX biogenesis in which maturation of newly translated COX SUI is initially assisted by CtaG, a chaperone implicated in CuB site metallation, followed by the interaction with the heme chaperone Surf1c to populate the redox-active metal-heme centers in SUI. Only then the remaining smaller subunits are recruited to form the mature enzyme which ultimately associates with respiratory complexes I and III into supercomplexes.

Bacterial Electron Transfer Chains Primed by Proteomics

Electron transport phosphorylation is the central mechanism for most prokaryotic species to harvest energy released in the respiration of their substrates as ATP. Microorganisms have evolved incredible variations on this principle, most of these we perhaps do not know, considering that only a fraction of the microbial richness is known. Besides these variations, microbial species may show substantial versatility in using respiratory systems. In connection herewith, regulatory mechanisms control the expression of these respiratory enzyme systems and their assembly at the translational and posttranslational levels, to optimally accommodate changes in the supply of their energy substrates. Here, we present an overview of methods and techniques from the field of proteomics to explore bacterial electron transfer chains and their regulation at levels ranging from the whole organism down to the Ångstrom scales of protein structures. From the survey of the literature on this subject, it is concluded that proteomics, indeed, has substantially contributed to our comprehending of bacterial respiratory mechanisms, often in elegant combinations with genetic and biochemical approaches. However, we also note that advanced proteomics offers a wealth of opportunities, which have not been exploited at all, or at best underexploited in hypothesis-driving and hypothesis-driven research on bacterial bioenergetics. Examples obtained from the related area of mitochondrial oxidative phosphorylation research, where the application of advanced proteomics is more common, may illustrate these opportunities.

Cooperation between two periplasmic copper chaperones is required for full activity of the cbb3 -type cytochrome c oxidase and copper homeostasis in Rhodobacter capsulatus

Copper (Cu) is an essential micronutrient that functions as a cofactor in several important enzymes, such as respiratory heme-copper oxygen reductases. Yet, Cu is also toxic and therefore cells engage a highly coordinated Cu uptake and delivery system to prevent the accumulation of toxic Cu concentrations. In this study, we analyzed Cu delivery to the cbb3 -type cytochrome c oxidase (cbb3 -Cox) of Rhodobacter capsulatus. We identified the PCuA C-like periplasmic chaperone PccA and analyzed its contribution to cbb3 -Cox assembly. Our data demonstrate that PccA is a Cu-binding protein with a preference for Cu(I), which is required for efficient cbb3 -Cox assembly, in particular, at low Cu concentrations. By using in vivo and in vitro cross-linking, we show that PccA forms a complex with the Sco1-homologue SenC. This complex is stabilized in the absence of the cbb3 -Cox-specific assembly factors CcoGHIS. In cells lacking SenC, the cytoplasmic Cu content is significantly increased, but the simultaneous absence of PccA prevents this Cu accumulation. These data demonstrate that the interplay between PccA and SenC not only is required for Cu delivery during cbb3 -Cox assembly but also regulates Cu homeostasis in R. capsulatus.