Neisseria gonorrhoeae causes the sexually transmitted infection gonorrhea, which is highly prevalent worldwide and has a major impact on reproductive and neonatal health. The superbug status of N. gonorrhoeae necessitates the development of drugs with different mechanisms of action. Here, we focused on targeting the nitrite reductase AniA, which is a pivotal component of N. gonorrhoeae anaerobic respiration and biofilm formation. Our studies showed that gonococci expressing AniA containing the altered catalytic residues D137A and H280A failed to grow under anaerobic conditions, demonstrating that the nitrite reductase function is essential. To facilitate the pharmacological targeting of AniA, new crystal structures of AniA were refined to 1.90-Å and 2.35-Å resolutions, and a phage display approach with libraries expressing randomized linear dodecameric peptides or heptameric peptides flanked by a pair of cysteine residues was utilized. Biopanning experiments led to the identification of 29 unique peptides, with 1 of them, C7-3, being identified multiple times. Evaluation of their ability to interact with AniA using enzyme-linked immunosorbent assay and computational docking studies revealed that C7-3 was the most promising inhibitor, binding near the type 2 copper site of the enzyme, which is responsible for interaction with nitrite. Subsequent enzymatic assays and biolayer interferometry with a synthetic C7-3 and its derivatives, C7-3m1 and C7-3m2, demonstrated potent inhibition of AniA. Finally, the MIC 50 value of C7-3 and C7-3m2 against anaerobically grown N. gonorrhoeae was 0.6 mM. We present the first peptide inhibitors of AniA, an enzyme that should be further exploited for antigonococcal drug development.
Mycobacterium tuberculosis (Mtb) has evolved numerous type VII secretion (ESX) systems to secrete multiple factors important for both growth and virulence across their cell envelope. ESX-1, ESX-3, and ESX-5 systems have been shown to each secrete a distinct set of substrates, including PE and PPE families of proteins, named for conserved Pro-Glu and Pro-Pro-Glu motifs in their N-termini. Proper secretion of the PE-PPE proteins requires the presence of EspG, with each system encoding its own unique copy. There is no cross-talk between any of the ESX systems and how each EspG is recognizing its subset of PE-PPE proteins is currently unknown. The only current structural characterization of PE-PPE-EspG heterotrimers is from the ESX-5 system. Here we present the crystal structure of the PE5mt-PPE4mt-EspG3mm heterotrimer from the ESX-3 system. Our heterotrimer reveals that EspG3mm interacts exclusively with PPE4mt in a similar manner to EspG5, shielding the hydrophobic tip of PPE4mt from solvent. The C-terminal helical domain of EspG3mm is dynamic, alternating between an ‘open’ and ‘closed’ form, and this movement is likely functionally relevant in the unloading of PE-PPE heterodimers at the secretion machinery. In contrast to the previously solved ESX-5 heterotrimers, the PE-PPE heterodimer of our ESX-3 heterotrimer is interacting with it’s chaperone at a drastically different angle, and presents different faces of the PPE protein to the chaperone. We conclude that the PPE-EspG interface from each ESX system has a unique shape complementarity that allows each EspG to discriminate amongst non-cognate PE-PPE pairs.
Phosphatase of Regenerating Liver-3 (PRL-3) is associated with cancer progression and metastasis. The mechanisms that drive PRL-3’s oncogenic functions are not well understood, partly due to a lack of research tools available to study this protein. We have begun to address these issues by developing alpaca-derived single domain antibodies, or nanobodies, targeting PRL-3 with a KD of 30–300 nM and no activity towards highly homologous family members PRL-1 and PRL-2. We found that longer and charged N-terminal tags on PRL-3, such as GFP and FLAG, changed PRL-3 localization compared to untagged protein, indicating that the nanobodies may provide new insights into PRL-3 trafficking and function. The nanobodies perform equally, if not better, than commercially available antibodies in immunofluorescence and immunoprecipitation. Finally, hydrogen-deuterium exchange mass spectrometry (HDX-MS) showed that the nanobodies bind partially within the PRL-3 active site and can interfere with PRL-3 phosphatase activity. Co-immunoprecipitation with a known PRL-3 active site binding partner, the CBS domain of metal transporter CNNM3, showed that the nanobodies reduced the amount of PRL-3:CBS inter-action. The potential of blocking this interaction is highly relevant in cancer, as multiple research groups have shown that PRL-3 binding to CNNM proteins is sufficient to promote metastatic growth in mouse models. The anti-PRL-3 nanobodies represent an important expansion of the research tools available to study PRL-3 function and can be used to define the role of PRL-3 in cancer progression.
Mycobacterium tuberculosis (Mtb) has evolved numerous type VII secretion (ESX) systems to secrete multiple factors important for both growth and virulence across their cell envelope. Three such systems; ESX-1, ESX-3, and ESX-5; have been shown to each secrete a unique set of substrates. A large class of these substrates secreted by these three systems are the PE and PPE families of proteins. Proper secretion of the PE-PPE proteins requires the presence of EspG, with each system encoding its own unique copy. There is no cross-talk between any of the ESX systems and how each EspG is recognizing its subset of PE-PPE proteins is currently unknown. The only current structural characterization of PE-PPE-EspG trimers is from the ESX-5 system. Here we present the crystal structure of the PE5mt-PPE4mt-EspG3mm trimer, from the ESX-3 system. Our trimer reveals that EspG3mm interacts exclusively with PPE4mt in a similar manner to EspG5, shielding the hydrophobic tip of PPE4mt from solvent. The C-terminal helical domain of EspG3mm is dynamic, alternating between an 'open' and 'closed' form, and this movement is likely functionally relevant in the unloading of PE-PPE heterodimers at the secretion machinery. In contrast to the previously solved ESX-5 trimers, the PE-PPE heterodimer of our ESX-3 trimer is interacting with it's chaperone at a drastically different angle, and presents different faces of the PPE protein to the chaperone. We conclude that the PPE-EspG interface from each ESX system has a unique shape complementarity that allows each EspG to discriminate amongst noncognate PE-PPE pairs.
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