LOca-1: A minimal calcium-activated arginyl-specific orthocaspase from the Loki's Castle hydrothermal vent field

Arsın, H.; Hribovsek, P.; Urich, L.; Fedoy, A.-E.; Stokke, R.; Mak, P.; Kaczorowska, A.-K.; ODonoghue, A. J.; Kaczorowski, T.; Steen, I. H.

doi:10.64898/2026.11.04.764195

bioRxiv · 10.64898/2026.11.04.764195

LOca-1: A minimal calcium-activated arginyl-specific orthocaspase from the Loki's Castle hydrothermal vent field

Arsın, H.·Hribovsek, P.·Urich, L.·Fedoy, A.-E.·Stokke, R.·Mak, P.·Kaczorowska, A.-K.·ODonoghue, A. J.·Kaczorowski, T.·Steen, I. H.

View original source ↗Export metadata ↓

Abstract

Orthocaspases are prokaryotic homologs of metacaspases within the C14 family of cysteine proteases, yet their biochemical properties and cellular roles remain poorly understood. Here, we report the discovery and comprehensive characterization of LOca-1, a metagenome-derived orthocaspase from the Loki's Castle hydrothermal vent field. LOca-1 consists primarily of a single, conserved p20 catalytic domain and undergoes calcium-dependent activation through cleavage at a conserved arginine residue. Once activated, LOca-1 displays strict arginyl-specific proteolytic activity and strong selectivity for residues surrounding the cleavage site. The enzyme is both thermoactive and thermostable, exhibiting maximal activity at 65 {degrees}C and a melting temperature of approximately 72 {degrees}C. Structural modelling revealed conservation of the catalytic core relative to plant metacaspases despite substantial sequence divergence. To our knowledge, LOca-1 is only the second biochemically characterized orthocaspase and the first reported from a deep-sea hydrothermal vent environment. LOca-1 expands the known biochemical diversity of prokaryotic metacaspase homologs and provides insights into the properties of a minimal p20-domain orthocaspase. Together, our findings establish LOca-1 as a thermostable, calcium-activated arginyl-specific orthocaspase and provide a foundation for future studies of orthocaspase function in prokaryotes.

Explore related subjects

molecular biology Preprint

Keep this discovery

Explore connections, maps & timelines

BibTeX RIS

Arsın, H., Hribovsek, P., Urich, L., Fedoy, A.-E., Stokke, R., Mak, P., Kaczorowska, A.-K., ODonoghue, A. J., Kaczorowski, T., Steen, I. H.. 2026-11-10. LOca-1: A minimal calcium-activated arginyl-specific orthocaspase from the Loki's Castle hydrothermal vent field. https://doi.org/10.64898/2026.11.04.764195

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

A TMEM175 Mutation Disrupts the Lysosomal-Mitochondrial Axis Causing Short QT Syndrome and Sudden Cardiac Death

Short QT Syndrome (SQTS) is a rare cardiac channelopathy characterized by abnormally short QTc intervals and increased sudden cardiac death (SCD) risk. Only 20-30% of SQTS cases have been linked to genetic mutations, typi-cally in surface membrane ion channels. We identified a novel lysosomal TMEM175 gene mutation (p.Arg377His) in 7 patients in a family with SQTS and SCD. Genetic analyses, including whole exome sequencing in the family and rare-variant burden testing in [~]118,000 UK Biobank participants, sug-gested an association between TMEM175 rare variants and QT interval short-ening. Functional studies in CRISPR-engineered mice and patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) revealed that TMEM175R377H causes shortened QT intervals and hastened repolariza-tion, respectively, as well an increased arrhythmia susceptibility. Isolated TMEM175R377H cardiomyocytes showed action potential duration (APD) abbre-viation, confirmed in whole TMEM175R377H mouse hearts and patient-specific iPSC-CM monolayers. In silico and electron microscopy studies showed that TMEM175R377H disrupts lysosomal-mitochondrial interactions, leading to mito-chondrial dysfunction, as evidenced by the reduced maximal respiration and spare respiratory capacity, with reduced ATP production, IKATP activation, and APD shortening. This mutation represents the first non-sarcolemmal ion chan-nel defect associated with SQTS and high SCD risk, potentially expanding the genetic landscape of the disease.

molecular biology↗

bioRxiv2026

Protecting host mitochondria with vitamin B3 preserves bioenergetics and thermogenesis during antibiotic treatment

Antibiotics that target bacterial translation can also impair mitochondrial function because mitochondria retain bacterial-like ribosomes. As antibiotic resistance continues to increase and the use of several broad-spectrum antibiotics has been limited by their mitochondrial toxicity, there is a growing need to understand their off-target effects in host physiology, and to identify strategies that can mitigate antibiotic-induced mitochondrial dysfunction. We demonstrate that antibiotic chloramphenicol (CA) induces a dose-dependent reduction in mitochondrial respiration and mitochondrial thermogenesis in Drosophila S2 cells, human HEK293T cells and in developing Drosophila larvae. In vivo, CA exposure triggers female-biased aberrant innate immune activation of hosts carrying naturally occurring mitochondrial rRNA variants. Metabolomic profiling revealed alterations in vitamin B3 metabolism in Drosophila during and following CA exposure. Among the vitamin B3 vitamers examined, nicotinamide (NAM) exhibited the strongest protective effect, mitigating the CA-induced impairments in mitochondrial respiration and thermogenesis, as well as aberrant immune activation. We identify mitochondrial thermogenesis as a previously unrecognized target of antibiotic-induced mitochondrial perturbation and a sensitive marker of mitochondrial stress. Furthermore, we demonstrate that co-supplementation of CA with NAM mitigates antibiotic-induced mitochondrial toxicity through evolutionarily conserved mitochondrial pathways. Finally, we establish Drosophila as a powerful model for investigating antibiotic-induced mitochondrial dysfunction and for developing therapeutic strategies to protect host mitochondria during antibiotic treatment.

molecular biology↗

bioRxiv2026

Replication-stress response shapes Leishmania genome plasticity through non-equivalent RAD9 and HUS1 functions.

Genome plasticity, manifested as gene copy-number variation and mosaic aneuploidy, enables adaptation in Leishmania , yet how genome-surveillance pathways shape this variation remains unclear. Here we show that partial depletion of HUS1 or RAD9, subunits of the conserved 9-1-1 checkpoint clamp, produces opposing replication-stress responses and contrasting patterns of genome remodelling in Leishmania major . During methotrexate selection HUS1 deficiency restricted DHFR-TS amplification and favoured linear amplicons, whereas RAD9 deficiency was associated with extensive circular amplification. This divergence extended to genome-wide scale: HUS1-deficient cells carried fewer but larger candidate rearrangements, whereas RAD9-deficient cells retained a largely wild-type rearrangement burden. These differences were accompanied by distinct HUS1 and RAD9 occupancy profiles around repetitive DNA implicated in gene amplification. Deficiency of either of these factors also resulted in differing effects on aneuploidy. While HUS1-deficient cells showed limited shifts towards chromosome disomy, RAD9-deficient cells exhibited broader chromosome copy-number gains and losses. Together, these findings identify replication-stress surveillance as a determinant of parasite genome plasticity, revealing that perturbing individual subunits of the same checkpoint complex can produce opposing genome-remodelling outcomes and reshape the variation available for adaptation.

molecular biology↗