Biology subjects

Dessen, A.

Publications and source records attributed to Dessen, A..

3 recordsLinked to original sources

bioRxiv2026

Dimeric Alix nucleates ESCRT-III CHMP4 polymerization

Alix is a key adaptor protein of the endosomal sorting complex required for transport (ESCRT) membrane remodeling machinery. Although Alix-mediated recruitment of the ESCRT-III subunit CHMP4 is well established, the molecular mechanisms underlying Alix activation and ESCRT-III polymerization remain poorly understood. Here, we present the crystal structure of the dimeric Alix V-domain (Alix-V) in complex with a llama nanobody. Dimerization is mediated by domain swapping, generating an X-shaped flexible conformation. We demonstrate that Alix forms dimers in vivo and provide evidence for the recruitment of dimeric Alix to plasma membrane repair sites and the cytokinetic midbody. Notably, a mutation disrupting Alix dimerization impairs plasma membrane repair. Furthermore, high-speed AFM experiments reveal that dimeric Alix, but not the monomeric form, nucleates CHMP4B filament polymerization. Our data establish that dimeric Alix is the active form responsible for nucleating two ESCRT-III CHMP4 filaments, whose geometry creates a platform for the recruitment of downstream ESCRT-III components required to assemble the active membrane remodeling and fission machinery.

biochemistry↗

bioRxiv2024

Protective human monoclonal antibodies that target the Type III Secretion System of Pseudomonas aeruginosa inhibit translocon function

Pseudomonas aeruginosa is a major human opportunistic pathogen associated with a high incidence of multi-drug resistance. The antibody-based blockade of P. aeruginosa virulence factors represents a promising alternative strategy to mitigate its infectivity. In this study, we employed single B cell sorting from cystic fibrosis patients to isolate human monoclonal antibodies (mAbs) targeting proteins from the P. aeruginosa Type 3 Secretion System (T3SS) and characterized a panel of mAbs directed at PscF and PcrV. Among those, two mAbs, P5B3 and P3D6, that bind to the injectisome tip protein PcrV, exhibited T3SS blocking activity. We solved the crystal structure of the P3D6 Fab-PcrV complex, which revealed that the Ab binds to the C-terminal region of PcrV. In addition, we compared the T3SS-blocking activity of three PcrV-targeting mAbs, including two from previous independent studies, using two distinct assays to evaluate pore formation and toxin injection. We conducted a mechanistic and structural analysis of their modes of action through modeling based on the known structure of a functional homolog, SipD from Salmonella typhimurium. The analysis suggests that anti-PcrV mAbs may act through different mechanisms, ranging from preventing PcrV oligomerization to disrupting PcrVs scaffolding function, thereby inhibiting the assembly and function of the translocon pore. Our findings provide additional evidence that T3SS-targeting Abs, some capable of inhibiting virulence, are elicited in P. aeruginosa-infected patients. The results offer deeper insights into PcrV recognition by mAbs and their associated mechanisms of action, helping to identify which Abs are more likely to be therapeutically useful based on their mode of action and potency. This paves the way for the development of effective alternatives to traditional antibiotics in the fight against this resilient pathogen.

microbiology↗

bioRxiv2019

An RNA-binding protein secreted by Listeria monocytogenes activates RIG-I signaling

Recent studies have reported on the presence of bacterial RNA within or outside extracellular membrane vesicles, possibly as ribonucleoprotein complexes. Proteins that bind and stabilize bacterial RNAs in the extracellular environment have not been reported. Here, we show that the bacterial pathogen Listeria monocytogenes secretes a small RNA binding protein that we named Zea. We show that Zea binds and stabilizes a subset of L. monocytogenes RNAs causing their accumulation in the extracellular medium. Furthermore, Zea binds RIG-I, the vertebrate non-self-RNA innate immunity sensor and potentiates RIG-I-signaling leading to interferon {beta} production. By performing in vivo infection, we finally show that Zea modulates L. monocytogenes virulence. Together, this study reveals that bacterial extracellular RNAs and RNA binding proteins can affect the host-pathogen crosstalk.

cell biology↗