The disulfide oxidoreductase SdbA is active in Streptococcus gordonii using a single C-terminal cysteine of the CXXC motif

Exploring the role of the disulfidptosis-related gene SLC7A11 in adrenocortical carcinoma: implications for prognosis, immune infiltration, and therapeutic strategies

BACKGROUND

Disulfidptosis and the disulfidptosis-related gene SLC7A11 have recently attracted significant attention for their role in tumorigenesis and tumour management. However, its association with adrenocortical carcinoma (ACC) is rarely discussed.

METHODS

Differential analysis, Cox regression analysis, and survival analysis were used to screen for the hub gene SLC7A11 in the TCGA and GTEx databases and disulfidptosis-related gene sets. Then, we performed an association analysis between SLC7A11 and clinically relevant factors in ACC patients. Univariate and multivariate Cox regression analyses were performed to evaluate the prognostic value of SLC7A11 and clinically relevant factors. Weighted gene coexpression analysis was used to find genes associated with SLC7A11. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses and the LinkedOmics database were used to analyse the functions of SLC7A11-associated genes. The CIBERSORT and Xcell algorithms were used to analyse the relationship between SLC7A11 and immune cell infiltration in ACC. The TISIDB database was applied to search for the correlation between SLC7A11 expression and immune chemokines. In addition, we performed a correlation analysis for SLC7A11 expression and tumour mutational burden and immune checkpoint-related genes and assessed drug sensitivity based on SLC7A11 expression. Immunohistochemistry and RT‒qPCR were used to validate the upregulation of SLC7A11 in the ACC.

RESULTS

SLC7A11 is highly expressed in multiple urological tumours, including ACC. SLC7A11 expression is strongly associated with clinically relevant factors (M-stage and MYL6 expression) in ACC. SLC7A11 and the constructed nomogram can accurately predict ACC patient outcomes. The functions of SLC7A11 and its closely related genes are tightly associated with the occurrence of disulfidptosis in ACC. SLC7A11 expression was tightly associated with various immune cell infiltration disorders in the ACC tumour microenvironment (TME). It was positively correlated with the expression of immune chemokines (CXCL8, CXCL3, and CCL20) and negatively correlated with the expression of immune chemokines (CXCL17 and CCL14). SLC7A11 expression was positively associated with the expression of immune checkpoint genes (NRP1, TNFSF4, TNFRSF9, and CD276) and tumour mutation burden. The expression level of SLC7A11 in ACC patients is closely associated withcthe drug sensitivity.

CONCLUSION

In ACC, high expression of SLC7A11 is associated with migration, invasion, drug sensitivity, immune infiltration disorders, and poor prognosis, and its induction of disulfidptosis is a promising target for the treatment of ACC.

Generation of False-Positive SARS-CoV-2 Antigen Results with Testing Conditions outside Manufacturer Recommendations: A Scientific Approach to Pandemic Misinformation

Antigen-based rapid diagnostics tests (Ag-RDTs) are useful tools for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection. However, misleading demonstrations of the Abbott Panbio coronavirus disease 2019 (COVID-19) Ag-RDT on social media claimed that SARS-CoV-2 antigen could be detected in municipal water and food products. To offer a scientific rebuttal to pandemic misinformation and disinformation, this study explored the impact of using the Panbio SARS-CoV-2 assay with conditions falling outside manufacturer recommendations. Using Panbio, various water and food products, laboratory buffers, and SARS-CoV-2-negative clinical specimens were tested with and without manufacturer buffer. Additional experiments were conducted to assess the role of each Panbio buffer component (tricine, NaCl, pH, and Tween 20) as well as the impact of temperature (4°C, 20°C, and 45°C) and humidity (90%) on assay performance. Direct sample testing (without the kit buffer) resulted in false-positive signals resembling those obtained with SARS-CoV-2 positive controls tested under proper conditions. The likely explanation of these artifacts is nonspecific interactions between the SARS-CoV-2-specific conjugated and capture antibodies, as proteinase K treatment abrogated this phenomenon, and thermal shift assays showed pH-induced conformational changes under conditions promoting artifact formation. Omitting, altering, and reverse engineering the kit buffer all supported the importance of maintaining buffering capacity, ionic strength, and pH for accurate kit function. Interestingly, the Panbio assay could tolerate some extremes of temperature and humidity outside manufacturer claims. Our data support strict adherence to manufacturer instructions to avoid false-positive SARS-CoV-2 Ag-RDT reactions, otherwise resulting in anxiety, overuse of public health resources, and dissemination of misinformation. IMPORTANCE With the Panbio severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antigen test being deployed in over 120 countries worldwide, understanding conditions required for its ideal performance is critical. Recently on social media, this kit was shown to generate false positives when manufacturer recommendations were not followed. While erroneous results from improper use of a test may not be surprising to some health care professionals, understanding why false positives occur can help reduce the propagation of misinformation and provide a scientific rebuttal for these aberrant findings. This study demonstrated that the kit buffer's pH, ionic strength, and buffering capacity were critical components to ensure proper kit function and avoid generation of false-positive results. Typically, false positives arise from cross-reacting or interfering substances; however, this study demonstrated a mechanism where false positives were generated under conditions favoring nonspecific interactions between the two antibodies designed for SARS-CoV-2 antigen detection. Following the manufacturer instructions is critical for accurate test results.

Identification of a Thiol-Disulfide Oxidoreductase (SdbA) Catalyzing Disulfide Bond Formation in the Superantigen SpeA in Streptococcus pyogenes

Mechanisms of disulfide bond formation in the human pathogen Streptococcus pyogenes are currently unknown. To date, no disulfide bond-forming thiol-disulfide oxidoreductase (TDOR) has been described and at least one disulfide bonded protein is known in S. pyogenes. This protein is the superantigen SpeA, which contains 3 cysteine residues (Cys 87, Cys90, and Cys98) and has a disulfide bond formed between Cys87 and Cys98. In this study, candidate TDORs were identified from the genome sequence of S. pyogenes MGAS8232. Using mutational and biochemical approaches, one of the candidate proteins, SpyM18_2037 (named here SdbA), was shown to be the catalyst that introduces the disulfide bond in SpeA. SpeA in the culture supernatant remained reduced when sdbA was inactivated and restored to the oxidized state when a functional copy of sdbA was returned to the sdbA-knockout mutant. SdbA has a typical C₄₆XXC₄₉ active site motif commonly found in TDORs. Site-directed mutagenesis experiments showed that the cysteines in the CXXC motif were required for the disulfide bond in SpeA to form. Interactions between SdbA and SpeA were examined using cysteine variant proteins. The results showed that SdbA_C49A formed a mixed disulfide with SpeA_C87A, suggesting that the N-terminal Cys46 of SdbA and the C-terminal Cys98 of SpeA participated in the initial reaction. SpeA oxidized by SdbA displayed biological activities suggesting that SpeA was properly folded following oxidation by SdbA. In conclusion, formation of the disulfide bond in SpeA is catalyzed by SdbA and the findings represent the first report of disulfide bond formation in S. pyogenes. IMPORTANCE Here, we reported the first example of disulfide bond formation in Streptococcus pyogenes. The results showed that a thiol-disulfide oxidoreductase, named SdbA, is responsible for introducing the disulfide bond in the superantigen SpeA. The cysteine residues in the CXXC motif of SdbA are needed for catalyzing the disulfide bond in SpeA. The disulfide bond in SpeA and neighboring amino acids form a disulfide loop that is conserved among many superantigens, including those from Staphylococcus aureus. SpeA and staphylococcal enterotoxins lacking the disulfide bond are biologically inactive. Thus, the discovery of the enzyme that catalyzes the disulfide bond in SpeA is important for understanding the biochemistry of SpeA production and presents a target for mitigating the virulence of S. pyogenes.

Identification of Redox Partners of the Thiol-Disulfide Oxidoreductase SdbA in Streptococcus gordonii

We previously identified a novel thiol-disulfide oxidoreductase, SdbA, in Streptococcus gordonii that formed disulfide bonds in substrate proteins and played a role in multiple phenotypes. In this study, we used mutational, phenotypic, and biochemical approaches to identify and characterize the redox partners of SdbA. Unexpectedly, the results showed that SdbA has multiple redox partners, forming a complex oxidative protein-folding pathway. The primary redox partners of SdbA that maintain its active site in an oxidized state are a surface-exposed thioredoxin family lipoprotein called SdbB (Sgo_1171) and an integral membrane protein annotated as CcdA2. Inactivation of sdbB and ccdA2 simultaneously, but not individually, recapitulated the sdbA mutant phenotype. The sdbB-ccdA2 mutant had defects in a range of cellular processes, including autolysis, bacteriocin production, genetic competence, and extracellular DNA (eDNA) release. AtlS, the natural substrate of SdbA produced by the sdbB-ccdA2 mutant lacked activity and an intramolecular disulfide bond. The redox state of SdbA in the sdbB-ccdA2 mutant was found to be in a reduced form and was restored when sdbB and ccdA2 were knocked back into the mutant. In addition, we showed that SdbB formed a disulfide-linked complex with SdbA in the cell. Recombinant SdbB and CcdA2 exhibited oxidase activity and reoxidized reduced SdbA in vitro Collectively, our results demonstrate that S. gordonii uses multiple redox partners for oxidative protein folding.IMPORTANCE Streptococcus gordonii is a commensal bacterium of the human dental plaque. Previously, we identified an enzyme, SdbA, that forms disulfide bonds in substrate proteins and plays a role in a number of cellular processes in S. gordonii Here, we identified the redox partners of SdbA. We showed that SdbA has multiple redox partners, SdbB and CcdA2, forming a complex oxidative protein-folding pathway. This pathway is essential for autolysis, bacteriocin production, genetic competence, and extracellular DNA (eDNA) release in S. gordonii These cellular processes are considered to be important for the success of S. gordonii as a dental plaque organism. This is the first example of an oxidative protein-folding pathway in Gram-positive bacteria that consists of an enzyme that uses multiple redox partners to function.

Disulfide bond formation in prokaryotes

Interest in protein disulfide bond formation has recently increased because of the prominent role of disulfide bonds in bacterial virulence and survival. The first discovered pathway that introduces disulfide bonds into cell envelope proteins consists of Escherichia coli enzymes DsbA and DsbB. Since its discovery, variations on the DsbAB pathway have been found in bacteria and archaea, probably reflecting specific requirements for survival in their ecological niches. One variation found amongst Actinobacteria and Cyanobacteria is the replacement of DsbB by a homologue of human vitamin K epoxide reductase. Many Gram-positive bacteria express enzymes involved in disulfide bond formation that are similar, but non-homologous, to DsbAB. While bacterial pathways promote disulfide bond formation in the bacterial cell envelope, some archaeal extremophiles express proteins with disulfide bonds both in the cytoplasm and in the extra-cytoplasmic space, possibly to stabilize proteins in the face of extreme conditions, such as growth at high temperatures. Here, we summarize the diversity of disulfide-bond-catalysing systems across prokaryotic lineages, discuss examples for understanding the biological basis of such systems, and present perspectives on how such systems are enabling advances in biomedical engineering and drug development.

Endogenous, regulatory cysteine sulfenylation of ERK kinases in response to proliferative signals

ERK-dependent signaling is key to many pathways through which extracellular signals are transduced into cell-fate decisions. One conundrum is the way in which disparate signals induce specific responses through a common, ERK-dependent kinase cascade. While studies have revealed intricate ways of controlling ERK signaling through spatiotemporal localization and phosphorylation dynamics, additional modes of ERK regulation undoubtedly remain to be discovered. We hypothesized that fine-tuning of ERK signaling could occur by cysteine oxidation. We report that ERK is actively and directly oxidized by signal-generated H₂O₂ during proliferative signaling, and that ERK oxidation occurs downstream of a variety of receptor classes tested in four cell lines. Furthermore, within the tested cell lines and proliferative signals, we observed that both activation loop-phosphorylated and non-phosphorylated ERK undergo sulfenylation in cells and that dynamics of ERK sulfenylation is dependent on the cell growth conditions prior to stimulation. We also tested the effect of endogenous ERK oxidation on kinase activity and report that phosphotransfer reactions are reversibly inhibited by oxidation by as much as 80-90%, underscoring the importance of considering this additional modification when assessing ERK activation in response to extracellular signals.

Disulfide Bonds: A Key Modification in Bacterial Extracytoplasmic Proteins

Disulfide bonds are a common posttranslational modification that contributes to the folding and stability of extracytoplasmic proteins. Almost all organisms, from eukaryotes to prokaryotes, have evolved enzymes to make and break these bonds. Accurate and efficient disulfide bond formation can be vital for protein function; therefore, the enzymes that catalyze disulfide bond formation are involved in multiple biological processes. Recent advances clearly show that oral bacteria also have the ability to from disulfide bonds, and this ability has an effect on a range of dental plaque-related phenotypes. In the gram-positive Streptococcus gordonii, the ability to form disulfide bonds affected autolysis, extracellular DNA release, biofilm formation, genetic competence, and bacteriocin production. In Actinomyces oris, disulfide bond formation is needed for pilus assembly, coaggregation, and biofilm formation. In other gram-positive bacteria, such as Enterococcus faecalis, disulfide bonds are formed in secreted bacteriocins and required for activity. In these oral bacteria, the enzymes that catalyze the disulfide bonds are quite diverse and share little sequence homology, but all contain a CXXC catalytic active site motif and a conserved C-terminal cis-proline, signature features of a thiol-disulfide oxidoreductase. Emerging evidence also indicates that gram-negative oral bacteria, such as Porphyromonas gingivalis and Tannerella forsythia, use disulfide bonds to stabilize their outer membrane porin proteins. Bioinformatic screens reveal that these gram-negative bacteria carry genes coding for thiol-disulfide oxidoreductases in their genomes. In conclusion, disulfide bond formation in oral bacteria is an emerging field, and the ability to form disulfide bonds plays an important role in dental plaque formation and fitness for the bacteria.

Mutation of the Streptococcus gordonii Thiol-Disulfide Oxidoreductase SdbA Leads to Enhanced Biofilm Formation Mediated by the CiaRH Two-Component Signaling System

Streptococcus gordonii is a commensal inhabitant of human oral biofilms. Previously, we identified an enzyme called SdbA that played an important role in biofilm formation by S. gordonii. SdbA is thiol-disulfide oxidoreductase that catalyzes disulfide bonds in secreted proteins. Surprisingly, inactivation of SdbA results in enhanced biofilm formation. In this study we investigated the basis for biofilm formation by the ΔsdbA mutant. The results revealed that biofilm formation was mediated by the interaction between the CiaRH and ComDE two-component signalling systems. Although it did not affect biofilm formation by the S. gordonii parent strain, CiaRH was upregulated in the ΔsdbA mutant and it was essential for the enhanced biofilm phenotype. The biofilm phenotype was reversed by inactivation of CiaRH or by the addition of competence stimulating peptide, the production of which is blocked by CiaRH activity. Competition assays showed that the enhanced biofilm phenotype also corresponded to increased oral colonization in mice. Thus, the interaction between SdbA, CiaRH and ComDE affects biofilm formation both in vitro and in vivo.

Thiol-Disulfide Exchange in Gram-Positive Firmicutes

Extracytoplasmic thiol-disulfide oxidoreductases (TDORs) catalyze the oxidation, reduction, and isomerization of protein disulfide bonds. Although these processes have been characterized in Gram-negative bacteria, the majority of Gram-positive TDORs have only recently been discovered. Results from recent studies have revealed distinct trends in the types of TDOR used by different groups of Gram-positive bacteria, and in their biological functions. Actinobacteria TDORs can be essential for viability, while Firmicute TDORs influence various physiological processes, including protein stability, oxidative stress resistance, bacteriocin production, and virulence. In this review we discuss the diverse extracytoplasmic TDORs used by Gram-positive bacteria, with a focus on Gram-positive Firmicutes.