Biology subjects

Katzenell, S.

Publications and source records attributed to Katzenell, S..

3 recordsLinked to original sources

bioRxiv2026

A bistable type III secretion system is primed and loaded in Pseudomonas aeruginosa hypervirulent isolates with positively selected codon changes in exsA or exsD

Pseudomonas aeruginosa has multiple virulence factors that promote airway infections in people with immune deficiencies. Most clinical isolates from human infections have functional type III secretion systems (T3SSs) that are subject to bistable regulation and secrete the cytotoxic effector ExoS into neutrophils. During airway infection in people with cystic fibrosis (CF), P. aeruginosa maintains bistable regulation or genetically adapts by inactivating or hyperactivating T3SS expression. CF clinical isolates with hyperactive T3SSs have codon changes in the transcriptional regulators, exsA or exsD. It is not known how these mutations: 1) arise, 2) promote hypervirulence, or 3) impact bistable T3SS regulation. To understand how these mutants arise, ~24,000 genomes in the NCBI Pathogens database were searched for positively selected mutations in exs genes based on nonsynonomous to synonymous codon change ratios. Missense and nonsense mutations were detected in exsA (47) or exsD (45) the majority of which are predicted to be positively selected. To determine how one of these codon changes promotes hypervirulence, an exsAT48I isolate was used to establish lung infections in mice engineered with a CF genotype. The exsAT48I mutant and an exsA+ control had similar lung burdens, but the former caused exacerbated weight loss and lung inflammation, suggesting immunopathology from phagocyte death as the cause of hypervirulence. Two additional hyperactive mutants were identified by screening a small collection of isolates from children with CF. Immunoblotting and fluorescence microscopy showed that hyperactive exsA or exsD mutants increased production of T3SS injectisomes and effectors, indicating they have locked on (primed and loaded) phenotypes. ExsA dimer modeling revealed that codon changes like T48I in the {beta}-barrel domain cause a conformational change that hyperactivates the transcription factor. These results define that hyperactive mutants are positively selected, hypervirulent due to lung inflammation, and have primed and loaded T3SSs.

microbiology↗

bioRxiv2025

Regulation of the innate immune response in human neurons by ICP34.5 maintains herpes simplex virus 1 latency

Herpes simplex virus 1 (HSV-1) establishes latent infections in sensory neurons, from which HSV sporadically reactivates due to external stress and other stimuli. Latency and reactivation are studied through in vivo models in a variety of hosts, as well as in vitro models using primary neurons, and neurons derived from pluripotent stem cells (iPSCs). These systems behave disparately, but the reasons remain unknown. The interferon (IFN)-based neuronal innate immune response is critical in controlling HSV-1 replication and HSV-1 counters these responses in part through infectedcell protein 34.5 (ICP34.5). ICP34.5 also promotes neurovirulence by preventing host translational shutoff and interfering with host cell autophagy. Here we demonstrate in a human iPSC neuronal model that sustaining host translation is the key activity of ICP34.5 for enhancement of reactivation. Specifically, our data shows that ICP34.5 was key for maintenance of HSV-1 latency. While interaction of ICP34.5 with the autophagy regulator Beclin 1 was important for maintaining latency, this was not due to modulation of bulk autophagy. Our work from primary mouse neurons suggested that the major effect of ICP34.5 on latency maintenance occurs in an IRF3/7-dependent manner. Notably, the role of ICP34.5 in regulating latency and reactivation differs between neurons derived from human iPSCs (iNeurons) and primary mouse trigeminal (TG) neurons. This highlights the importance of selecting an appropriate neuronal model and validating experimental outcomes in multiple models.

immunology↗

bioRxiv2020

The third coiled coil domain of Atg11 is required for shaping mitophagy initiation sites

Selective autophagy is the capture of specific cytosolic contents in double membrane vesicles that subsequently fuse with the vacuole or lysosome, thereby delivering cargo for degradation. Selective autophagy receptors (SARs) mark the cargo for degradation and, in yeast, recruit Atg11, the scaffolding protein for selective autophagy initiation. The mitochondrial protein Atg32 is the yeast SAR that mediates mitophagy, the selective autophagic capture of mitochondria. Atg11- Atg32 interactions concentrate Atg32 into puncta that are thought to represent sites of mitophagy initiation. However, it is unclear how Atg11 concentrates Atg32 to generate mitophagy initiation sites. We show here that the coiled coil 3 (CC3) domain of Atg11 is required for concentrating Atg32 into puncta. We determined the structure of the majority of the CC3, demonstrating that the CC3 forms a parallel homodimer whose dimer interface is formed by a small number of hydrophobic residues. We further show that the CC3 dimerization interface is required for shaping Atg32 into functional mitophagy initiation sites and for delivery of mitochondria to the vacuole. Our findings suggest that Atg11 self-interactions help concentrate SARs as a necessary precondition for cargo capture.

cell biology↗