Conserved copper(I)-binding auxiliary domains link virulence-associated LPMOs to copper homeostasis in the intestinal environment

Helicolysins emerge as a new family of metzincin metallopeptidases in host-pathogen interactions.

The Hom family and canilysin are defined as helicolysins, a previously uncharacterized metzincin subfamily distinguished by a conserved Thr-turn and an accessory ND, and implicates these proteins in host-pathogen interactions, adhesion, and immunomodulation.

Ant abaecin-2 is a context-dependent copper-binding effector that can be either inhibitory or protective

Host defense peptides (HDPs) are important components of the innate immune system that are used to combat pathogens and often rely on binding trace nutrient metals for their function. However, controlling nutrient metals may have other roles in host–symbiont interactions beyond poisoning harmful pathogens. This study characterizes the evolution, structural properties, and biochemical activity of the novel hymenopteran HDP abaecin-2. In myrmicine ants such as the fungus-growing tribe Attini, abaecin-2 has evolved to include an Amino-Terminal Cu(ii) and Ni(ii)-binding (ATCUN) motif, which we hypothesize binds copper, a trace nutrient that is enriched in attine ant colonies. Combined results from mass spectrometry, competitive binding assays, circular dichroism, and NMR indicate that the abaecin-2 peptide lacks a defined secondary structure and can associate with up to 2 Cu(ii) ions, one strongly bound at the ATCUN motif and another weakly bound, likely at a conserved histidine residue. Despite its copper-binding activity, abaecin-2 alone does not exhibit antibacterial activity against Escherichia coli or Bacillus subtilis (models for bacteria that live in ant fungus gardens). However, it synergizes with a model pore-forming peptide cecropin A to inhibit the growth of E. coli, similar to the related peptide abaecin-1. The copper-binding activity conferred by the ATCUN motif also protects copper-sensitive E. coli from excess copper toxicity. The dual context-dependent inhibitory and protective roles for abaecin-2 indicate that this previously under-characterized HDP may be used by attine ants to regulate both harmful and beneficial symbionts.

A cryptic aromatic binding pocket in the highly thermostable GpgS from Mycobacterium hassiacum hints at MGLP pathway crosstalk

The findings establish M. hassiacum as a valuable model for structural enzymology in mycobacteria and highlight GpgS as a potential drug target, opening new avenues for the development of inhibitors targeting this key, potentially pleiotropic enzyme.

PoGPx-7, a glutathione peroxidase homolog from teleosts, exhibits bactericidal activity and activates host immune cells against bacterial infection.

In mammals, glutathione peroxidase 7 (GPx-7) is a member of the GPx family that exhibits peroxidase activity. Its immunological functions, especially in host defense against bacterial infection, remain unexplored in lower vertebrates. In this study, we identified a GPx-7 homolog from Paralichthys olivaceus (PoGPx-7) and investigated its roles during Vibrio alginolyticus infection. PoGPx-7 possesses a conserved GSH-Px domain and carries positive net charges. PoGPx-7 was constitutively expressed in various tissues, with significant upregulation upon bacterial challenge. Recombinant PoGPx-7 (rPoGPx-7) exhibited GPx activity and bound to V. alginolyticus via interaction with lipopolysaccharide and peptidoglycan. In addition, rPoGPx-7 could directly kill bacteria by disrupting membrane integrity, leading to severe structural damage and content leakage. The bactericidal activity was modulated by protein concentration, pH, temperature, and Zn2+. Furthermore, rPoGPx-7 bound to peripheral blood leukocytes (PBLs), reduced bacterial attachment and LDH release, and protected PBLs from cell death. It also significantly enhanced phagocytosis, respiratory burst, and acid phosphatase activity of PBLs. In vivo administration showed that rPoGPx-7 reduced bacterial loads in the tissues, and improved fish survival, whereas knockdown of PoGPx-7 increased susceptibility to infection. These findings provide the first evidence that teleosts GPx-7 functions as a dual-effector molecule with direct bactericidal activity and immunomodulatory capacity, providing an immunological insight of GPx family members on resistance bacterial infection.

A Poly(rC)-Binding Protein Mediates Iron Delivery to Ferritin in Anopheles stephensi

A broad-spectrum phage-encoded mechanism to disarm bacterial type IV filaments

Phages can modify host cell physiology to thwart competitors. The Pseudomonas aeruginosa-specific phage DMS3 encodes Aqs1, a protein inhibitor of type IV pilus (T4P) function to prevent host cell recognition by other phages that leverage these filaments for infection. Aqs1 disrupts T4P by binding to the hexameric ATPase PilB, required to power pilus filament extension, though several mechanistic details remain unclear. We show that Aqs1 has broad-spectrum activity and can disrupt T4P function in a variety of Gram negative bacteria. This protein inhibits PilB by binding to a solvent-exposed hydrophobic patch on the N2-domain, distal to the active site. Binding destabilizes the hexamer, preventing PilB accumulation at T4P machines. Aqs1 likely disrupts PilB oligomerization by displacing a flexible linker segment between the PilB N1- and N2-domains required for inter-subunit contact. Together, the Aqs1 mode of action provides a design template for broad-spectrum inhibitors of diverse bacterial virulence factors. Significance The phage-encoded protein Aqs1 disables type IV pilus (T4P) production in Pseudomonas aeruginosa by targeting the hexameric ATPase responsible for assembling pilus fibers. We show that despite originating from a P. aeruginosa-specific phage, Aqs1 can also disable T4 ATPase-dependent phenotypes across other pathogenic bacteria and homologous systems. Mechanistically, Aqs1 binds to a conserved patch on the PilB N2-domain away from the active site. Binding here breaks apart the PilB oligomer, preventing it from acting on T4P machines. Aqs1 binding at the N2-domain patch likely displaces a flexible PilB linker segment that binds to this site to stabilize the hexamer. Our work highlights a novel and conserved PilB allosteric site which is exploited by the phage-encoded protein Aqs1 to disrupt diverse T4 systems in multiple bacteria.