The outer-membrane protein MafA of Neisseria meningitidis constitutes a novel protein secretion pathway specific for the fratricide protein MafB

Abstract

MafB proteins are toxins secreted by Neisseria spp. which are involved in interbacterial competition. Their secretion mechanism has so far not been elucidated. Each strain can produce several MafB variants. On the chromosome, the mafB genes are localized on genomic islands also containing mafA genes. MafA proteins have a role in virulence with reported activities in adhesion and transcytosis of pathogenic Neisseria, a priori unrelated to MafB activities. In this study, we investigated the possible involvement of MafA in the transport of MafB across the outer membrane of Neisseria meningitidis . In wild-type strains, proteolytic fragments of MafB proteins were detected in the extracellular medium. In the absence of MafA, secretion was abrogated, and, in the case of MafB I , full-length and truncated polypeptides were detected inside the cells and inside outer-membrane vesicles. MafB I secretion required its cognate MafA, whereas MafB III could use any MafA. Heterologous expression in Escherichia coli showed that MafB III is transported to a cell-surface-exposed, i.e. protease-accessible, location in a MafA-dependent way. MafA itself was found to be localized to the outer membrane, forming large oligomeric complexes. As homologs were found in diverse bacteria, the Maf system represents a new protein secretion system in Gram-negative bacteria.

Comparative Whole-Genome Analysis of Neisseria gonorrhoeae Isolates Revealed Changes in the Gonococcal Genetic Island and Specific Genes as a Link to Antimicrobial Resistance

“…In particular, ST 225 was characterized by the presence of MafB, a toxin for the defense against other bacteria, as well as a protein of the Sel1 repeat family, which plays an important role in iron metabolism. For type 807, the mafA gene, whose expression products are involved in virulence, adhesion and transcytosis in pathogenic Neisseria and are necessary for the function of MafB (Arenas et al, 2020), was notable.…”

“…The genes specific to ST 807 included a gene encoding the multiple adhesin family protein MafA, whose expression products are involved in virulence, adhesion and transcytosis in pathogenic Neisseria and are required for the function of the polymorphic toxin MafB (Arenas et al, 2020); a gene encoding a protein of the ComF family and required for transformation (Tribble et al, 2012); an M48 family metallopeptidase gene; a gene encoding a protein of the thermonuclease family belonging to the replication, recombination and repair system; a gene encoding the modification methylase ModA (restrictionmodification system); which is involved in the control of phase variations in representatives of the Neisseria genus (Gawthorne et al, 2012); and a gene encoding an AAA family ATPase that may act as a toxin for a type IV toxin-antitoxin resistance system (Yamamoto et al, 2009). We also identified a number of specific genes that constituted the GGI, in particular, traG, eppA, and ych1, in which alterations or lesions have occurred (premature stop codons or reading frameshifts).…”

“…For ST 1407, the specific genes included a type XXXIV mosaic allele of the penA gene encoding the PBP 2 protein, whose presence reduces the susceptibility of N. gonorrhoeae to b-lactam drugs, and genes encoding the opacity protein and the MafB family polymorphic toxin HNH endonuclease (Jamet and Nassif, 2015;Arenas et al, 2020).…”

Biofilms as Promoters of Bacterial Antibiotic Resistance and Tolerance

“…TpsA induces persister formation upon direct contact with cells lacking sufficient levels of immunity protein [179]. Very likely, more recently discovered secretion systems that deliver toxins to the target cells [180,181] also contribute to biofilm formation and recalcitrance, a research area that needs to be addressed.…”

Et tu, Neisseria? Conflicts of Interest Between Neisseria Species

“…Original observations that MafB could be detected in culture supernatants in the absence of a MafA led to speculation that the toxins may be secreted by association with outer membrane vesicles (Jamet et al, 2015). A later study revealed that MafA mediates MafB translocation across the outer membrane, and after secretion MafB can undergo further maturation via auto-proteolysis of a HINT domain (Arenas et al, 2020). In contrast, the path of entry of secreted toxins into target cells is poorly understood and merits further study.…”