Biology subjects

Szabo, M.

Publications and source records attributed to Szabo, M..

8 recordsLinked to original sources

bioRxiv2026

FAM136A is an essential chaperone for mitochondrial membrane protein biogenesis

The metabolic and signaling function of mitochondria rely on a network of chaperones within the inner membrane space (IMS) that regulate the biogenesis of nascent mitochondrial proteins. Using a genome wide CRISPRi screen we found that in human cells FAM136A is required for biogenesis of all three voltage-dependent anion channel (VDAC) paralogs, an abundant and essential family of {beta}-barrel metabolite transporters in the outer mitochondrial membrane (OM). FAM136A is a ubiquitously expressed essential gene, that is conserved in metazoa and plants. Using a combination of experiments in human cells and in vitro reconstitution, we determined that FAM136A associates with unfolded VDACs in the IMS; solubilizes nascent VDAC through a direct interaction; and facilitates insertion of VDAC into the OM. FAM136A also binds and chaperones a subset of -helical subunits of the electron transport chain. We therefore conclude that FAM136A is an IMS-resident chaperone, necessary and sufficient to maintain nascent membrane proteins in a folding-competent state to mediate their integration into the bilayer.

molecular biology↗

bioRxiv2025

Extracellular electron transport in coral-algal symbiosis studied by chlorophyll fluorescence relaxation and ferricyanide reduction

Coral health depends on intricate metabolic interactions between the coral host and its symbiotic algae, Symbiodiniaceae. While nutrient exchange is well established, electron-level interactions have remained unexplored. Here, we provide evidence for extracellular electron transport (EET) within coral-algal symbiosis, supported by variable chlorophyll (Chl) fluorescence and ferricyanide reduction measurements. We observed a slow wave in the relaxation of flash-induced Chl fluorescence kinetics under microaerobic conditions in both isolated Fugacium kawagutii (CS156) cells and intact corals, reflecting redox dynamics of the primary quinone electron acceptor (QA) in the photosynthetic electron transport chain. The addition of the extracellular electron acceptor ferricyanide decreased the wave amplitude and QA reduction while being reduced to ferrocyanide, demonstrating EET from the symbiont to extracellular acceptors. Slower Chl fluorescence rise kinetics under continuous illumination in intact corals compared to isolated symbionts indicate that electrons may also flow from symbionts to the host. Under low oxygen conditions, QA was gradually reduced in corals in darkness but not in isolated symbiont cultures, suggesting electron transfer from host to symbiont. Together, these results indicate bidirectional extracellular electron exchange between symbiotic partners, pointing to a previously unrecognized mechanism for redox balancing in coral-algal symbiosis. This pathway likely contributes to metabolic resilience and the maintenance of coral health under fluctuating environmental conditions.

plant biology↗

bioRxiv2025

Dynamic exchange of antimicrobial peptides stabilize persistent lipid pores

Antimicrobial peptides (AMPs) are a promising broad-spectrum complement to conventional antibiotics. But despite their relatively simple structures, the reported modes of action of AMPs are diverse, ranging from formation of stable ion-channel-like structures, or disruption of biochemical pathways, to comprehensive membrane solubilization. This apparent complexity of function is a significant hurdle in their future application and rational design. Here, we combine single-molecule tracking with optical single-channel recording in synthetic mimics of bacterial membranes to image the pores formed by AMPs in real time, mapping the diffusion of individual AMPs relative to sites of membrane permeablization. Using alamethicin, magainin-II and melittin as archetypes of three principal membrane-disrupting AMP classes, we observe AMP molecules freely diffusing on the membrane, but with an enhancement of local peptide surface density within a nanoscopic region surrounding each pore locus. We do not observe this enhancement for indolicidin, an AMP which is not believed to use pore formation as its main mode of toxicity. Corroborated by molecular dynamics simulations that replicate our experiments, these results suggest defects formed by membrane-active AMPs are persistent but dynamic structures, stabilised by individual peptides free to diffuse into and out of the pore. Whilst alamethicin, magainin-II and melittin are often placed in different mechanistic pore-forming groups, the broad similarities between observations in these different AMPs encourages a continuum view of pore-forming ability, rather than discrete categories of mechanism.

biophysics↗

bioRxiv2025

Unprecedented exoelectrogenic activity in Parachlorella kessleri MACC-38: The interplay of photosynthetic electron transport and the oxidative pentose phosphate pathway

Exoelectrogenesis is the ability of living cells to export electrons. In photosynthetic organisms, exoelectrogenesis is of particular interest because it can be used for transduction of solar energy into electric current in biophotovoltaics or reducing power for biocatalysis. Previously, we identified and characterized the green microalga Parachlorella kessleri MACC-38 producing unprecedented current largely dependent on the photosynthetic electron transport chain (PETC). In this study, our comparative photosynthetic characterization demonstrates that chlororespiration is a crucial factor maintaining the PETC redox balance in MACC-38. Our data points that the oxidative pentose phosphate pathway (OPPP) is activated during exoelectrogenesis to meet the increased demand of reducing power. We hypothesize that chlororespitration prevents oversaturation of PETC during OPPP activation. These findings provide valuable insights into the fundamental mechanisms of exoelectrogenesis in green algae. By elucidating the complex interconnection between PETC, OPPP and exoelectrogenesis, our results pave the way towards improved bioelectrochemical and biocatalysis technologies.

plant biology↗

bioRxiv2023

Photo-physiological Acclimation in Synechocystis sp. PCC 6803 Provides Insight into Growth Limitation in Underwater Spectra

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality has been missing. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 through the whole range of photosynthetically active radiation (PAR). Using LEDs with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes fine-tuning light capture such as state transitions and efficiency of energy transfer from phycobilisomes to photosystems. We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the PQ pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

plant biology↗

bioRxiv2023

Circulation of enterotoxigenic Escherichia coli (ETEC) isolates expressing CS23 from the environment to clinical settings

Enterotoxigenic Escherichia coli (ETEC) is one of the leading causes of infant diarrhea in low- and middle-income countries (LMICs). Diarrheal pathogens are transmitted through environmental reservoirs; however, the bacterial clones that spread across the human-environment interphases remind unexplored. We aimed to determine the relationship and clonal dissemination of ETEC between children with diarrhea (> 5 years of age) and polluted water samples from local river in La Paz, Bolivia. Our study used whole genome sequencing and phenotypic fingerprinting system (PhenePlates) to analyze ETEC strains. We showed that ST218 and ST410 LT+STh CS23 ETEC were found with high frequency in both samples. The CS23 ETEC isolates were found within several STs, E. coli phylogroups A, B1, C, and D, and across ETEC lineages. Our comparative genomic analysis and PhenePlate screening of globally distributed clinical ETEC strains suggested that virulent CS23 plasmids acquisition occurs independently of the bacterial chromosomal background. Environmental strains were more often multidrug-resistant (MDR) than clinical isolates and harbored the class 1 integron-integrase gene intI1 next to the MDR cassettes. Retrospective analysis of antibiotic resistance in ETEC revealed a high frequency of MDR in clinical isolates. The LT+STh CS23 ETEC isolates showed an increased biofilm ability at environmental temperature, equal cytotoxicity, and significantly lower adherence to human epithelial cells compared to ETEC expressing other CFs. Together, our findings suggest that CS23 is more prevalent in ETEC than previously estimated, and the Choqueyapu River is a reservoir for LT+STh CS23 ETEC containing strains capable of causing diarrheal cases in children. ImportanceThe importance of clean water cannot be overstated. It is a vital resource for maintaining health and well-being. Unfortunately, water sources contaminated with fecal discharges from animal and human origin due to a lack of wastewater management poses a significant risk to communities, as they can become a means of transmission pathogenic bacteria like enterotoxigenic E. coli (ETEC). ETEC is frequently found in polluted water in countries with a high prevalence of diarrheal diseases, such as Bolivia. This study provides novel insights into the circulation of ETEC between diarrheal cases and polluted water sources in areas with high rates of diarrheal disease. The findings highlight the Choqueyapu River as a potential reservoir for emerging pathogens carrying antibiotic-resistance genes, making it a crucial area for monitoring and intervention. Furthermore, the results demonstrate the feasibility of a low-cost, high-throughput method for tracking bacterial pathogens in low- and middle-income countries, making it a valuable tool for One Health monitoring efforts.

microbiology↗

bioRxiv2021

The Alzheimer's gene SORL1 is a key regulator of endosomal recycling in human neurons

BackgroundLoss of the Sortilin-related receptor 1 (SORL1) gene seems to act as a causal event for Alzheimers disease (AD). Recent studies have established that loss of SORL1, as well as mutations in autosomal dominant AD genes APP and PSEN1/2, pathogenically converge by swelling early endosomes, ADs cytopathological hallmark. Acting together with the retromer trafficking complex, SORL1 has been shown to regulate the recycling of the amyloid precursor protein (APP) out of the endosome, contributing to endosomal swelling and to APP misprocessing. We hypothesized that SORL1 plays a broader role in neuronal endosomal recycling and used human induced pluripotent stem cell derived neurons (hiPSC-Ns) to test this hypothesis. We examined endosomal recycling of three transmembrane proteins linked to AD pathophysiology: APP, the BDNF receptor Tropomyosin-related kinase B (TRKB), and the glutamate receptor subunit AMPA1 (GLUA1). MethodsWe used isogenic hiPSCs engineered to have SORL1 depleted or to have enhanced SORL1 expression. We differentiated neurons from these cell lines and mapped the trafficking of APP, TRKB and GLUA1 within the endosomal network using confocal microscopy. We also performed cell surface recycling and lysosomal degradation assays to assess the functionality of the endosomal network in both SORL1 depleted and overexpressing neurons. Finally, we analyzed alterations in gene expression in SORL1 depleted neurons using RNA-sequencing. ResultsWe find that as with APP, endosomal trafficking of GLUA1 and TRKB is impaired by loss of SORL1. We show that trafficking of all three cargo to late endosomes and lysosomes is affected by manipulating SORL1 expression. We also show that depletion of SORL1 significantly impacts the endosomal recycling pathway for APP and GLUA1 at the level of the recycling endosome and trafficking to the cell surface. This has a functional effect on neuronal activity as shown by multi-electrode array (MEA). Conversely, increased SORL1 expression enhances endosomal recycling for APP and GLUA1. Our unbiased transcriptomic data further support SORL1s role in endosomal recycling. We observe altered expression networks that regulate cell surface trafficking and neurotrophic signaling in SORL1 depleted neurons. ConclusionCollectively, and together with other recent observations, these findings suggest that SORL1 is a broad regulator of retromer-dependent endosomal recycling in neurons, a conclusion that has both pathogenic and therapeutic implications for Alzheimers disease.

cell biology↗

bioRxiv2020

Depletion of the AD risk gene SORL1 selectively impairs neuronal endosomal traffic independent of amyloidogenic APP processing

The SORL1 gene encodes for the protein SorLA, a sorting receptor involved in retromer-related endosomal traffic. Many SORL1 genetic variants increase Alzheimers disease (AD) risk, and rare loss-of-function truncation mutations have been found to be causal of late-onset AD. SORL1 is expressed in neurons and glia of the central nervous system and loss of SORL1 has been reported in AD tissue. To model the causal loss-of-function mutations, we used CRISPR/Cas9 technology to deplete SORL1 in human induced pluripotent stem cells (hiPSCs) to test the hypothesis that loss of SORL1 contributes to AD pathogenesis by leading to endosome dysfunction. We report that loss of SORL1 in hiPSC-derived neurons leads to early endosome enlargement, a cellular phenotype that is indicative of traffic jams and is now considered a hallmark cytopathology AD. We validate defects in neuronal endosomal traffic by showing decreased localization of amyloid-precursor protein (APP) in the trans-Golgi network (TGN), and increased localization of APP in early endosomes, a site of APP cleavage by the {beta} secretase BACE1. Microglia, immune cells of the CNS, which play a role in AD pathology also express SORL1. We therefore tested and found no effect of SORL1 depletion on endosome size or morphology in hiPSC-derived microglia, suggesting a selective effect on neuronal endosomal trafficking. Finally, because BACE1 dependent APP fragments can cause endosome enlargement, we treated SORL1 deficient hiPSC-derived neurons with BACE1 inhibitors and demonstrate that endosome enlargement occurs independent of amyloidogenic APP fragments. Collectively, these findings clarify where and how SORL1 links to AD. Moreover, our data, together with recent findings, underscores how sporadic AD pathways that regulate endosomal trafficking, and autosomal-dominant AD pathways that regulate APP cleavage, independently converge on the defining cytopathology of AD.

cell biology↗