Sulfate reducers have developed a multifaceted adaptative strategy to survive against oxidative stresses. Along with this oxidative stress response, we recently characterized an elegant reversible disulfide bond-dependent protective mechanism in the pyruvate:ferredoxin oxidoreductase (PFOR) of various Desulfovibrio species. Here, we searched for thiol redox systems involved in this mechanism. Using thiol fluorescent labeling, we show that glutathione is not the major thiol/disulfide balancecontrolling compound in four different Desulfovibrio species and that no other plentiful low molecular weight thiol can be detected. Enzymatic analyses of two thioredoxins (Trxs) and three thioredoxin reductases allow us to propose the existence of two independent Trx systems in Desulfovibrio vulgaris Hildenborough (DvH). The TR1/Trx1 system corresponds to the typical bacterial Trx system. We measured a TR1 apparent K m value for Trx1 of 8.9 M. Moreover, our results showed that activity of TR1 was NADPH-dependent. The second system named TR3/Trx3 corresponds to an unconventional Trx system as TR3 used preferentially NADH (K m for NADPH, 743 M; K m for NADH, 5.6 M), and Trx3 was unable to reduce insulin. The K m value of TR3 for Trx3 was 1.12 M. In vitro experiments demonstrated that the TR1/Trx1 system was the only one able to reactivate the oxygen-protected form of Desulfovibrio africanus PFOR. Moreover, ex vivo pulldown assays using the mutant Trx1 C33S as bait allowed us to capture PFOR from the DvH extract. Altogether, these data demonstrate that PFOR is a new target for Trx1, which is probably involved in the protective switch mechanism of the enzyme.Oxidative stress is a universal phenomenon experienced by both aerobic and anaerobic organisms from all three domains of life (1-3). To combat this problem, anaerobes have evolved multifaceted strategies to manage the deleterious effects of oxygen (O 2 ) exposure. In this regard, these organisms demonstrate varying degrees of tolerance to O 2 , ranging from the extremely sensitive methanogens, which typically are inhibited by only a few ppm of O 2 (4), to the much more aerotolerant Bacteroides (5) or sulfate-reducing Desulfovibrio species (6, 7). The extreme aerotolerance of these anaerobes can be related to their way of life. Abundance and metabolic activity of sulfate reducers in oxic zones of numerous biotopes (reviewed in Ref. 8) are frequently evaluated as higher than the ones found in neighboring anoxic zones. From the last decade, studies have uncovered original and complex adaptative strategies by which sulfate reducers seek to minimize the damage induced by oxidative conditions (8). One example is superoxide reductase, which is specific to anaerobes and scavenges superoxide ions by reduction. Although this enzyme is broadly distributed in sulfatereducing bacteria (9 -12), more species-specific mechanisms are also found as the disulfide bond-mediated protection of the pyruvate:ferredoxin oxidoreductase (PFOR) 3 (13). In Desulfovibrio africanus, this enzyme, which cont...

A novel class of molecular chaperones co‐ordinates the assembly and targeting of complex metalloproteins by binding to an amino‐terminal peptide of the cognate substrate. We have previously shown that the NarJ chaperone interacts with the N‐terminus of the NarG subunit coming from the nitrate reductase complex, NarGHI. In the present study, NMR structural analysis revealed that the NarG(1–15) peptide adopts an α‐helical conformation in solution. Moreover, NarJ recognizes and binds the helical NarG(1–15) peptide mostly via hydrophobic interactions as deduced from isothermal titration calorimetry analysis. NMR and differential scanning calorimetry analysis revealed a modification of NarJ conformation during complex formation with the NarG(1–15) peptide. Isothermal titration calorimetry and BIAcore experiments support a model whereby the protonated state of the chaperone controls the time dependence of peptide interaction. Structured digital abstract • http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-7557484: NarJT (uniprotkb:http://www.ebi.uniprot.org/entry/P0AF26) and NarG (uniprotkb:http://www.ebi.uniprot.org/entry/P09152) bind (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407) by isothermal titration calorimetry (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0065) • http://mint.bio.uniroma2.it/mint/search/interaction.do?interactionAc=MINT-7557456: NarJT (uniprotkb:http://www.ebi.uniprot.org/entry/P0AF26) and NarG (uniprotkb:http://www.ebi.uniprot.org/entry/P09152) bind (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0407) by nuclear magnetic resonance (http://www.ebi.ac.uk/ontology-lookup/?termId=MI:0077)

Galectins are glycan-binding proteins involved in various biological processes including cell/cell interactions. During B-cell development, bone marrow stromal cells secreting galectin-1 (GAL1) constitute a specific niche for pre-BII cells. Besides binding glycans, GAL1 is also a pre-B cell receptor (pre-BCR) ligand that induces receptor clustering, the first checkpoint of B-cell differentiation. The GAL1/pre-BCR interaction is the first example of a GAL1/unglycosylated protein interaction in the extracellular compartment. Here we show that GAL1/pre-BCR interaction modifies GAL1/glycan affinity and particularly inhibits binding to LacNAc containing epitopes. GAL1/pre-BCR interaction induces local conformational changes in the GAL1 carbohydrate-binding site generating a reduction in GAL1/glycan affinity. This fine tuning of GAL1/glycan interactions may be a strategic mechanism for allowing pre-BCR clustering and pre-BII cells departure from their niche. Altogether, our data suggest a novel mechanism for a cell to modify the equilibrium of the GAL1/glycan lattice involving GAL1/unglycosylated protein interactions.

Human Galectin-3 is found in the nucleus, the cytoplasm and at the cell surface. This lectin is constituted of two domains: an unfolded N-terminal domain and a C-terminal Carbohydrate Recognition Domain (CRD). There are still uncertainties about the relationship between the quaternary structure of Galectin-3 and its carbohydrate binding properties. Two types of self-association have been described for this lectin: a C-type self-association and a N-type self-association. Herein, we have analyzed Galectin-3 oligomerization by Dynamic Light Scattering using both the recombinant CRD and the full length lectin. Our results proved that LNnT induces N-type self-association of full length Galectin-3. Moreover, from Nuclear Magnetic Resonance (NMR) and Surface Plasmon Resonance experiments, we observed no significant specificity or affinity variations for carbohydrates related to the presence of the N-terminal domain of Galectin-3. NMR mapping clearly established that the N-terminal domain interacts with the CRD. We propose that LNnT induces a release of the N-terminal domain resulting in the glycan-dependent self-association of Galectin-3 through N-terminal domain interactions.