https://dspace.jcu.cz/handle/20.500.14390/41786 Wed, 15 Apr 2026 07:53:24 GMT 2026-04-15T07:53:24Z https://dspace.jcu.cz/handle/20.500.14390/47550 Exciton Delocalization Promotes Far-Red Absorption in a Tetrameric Chlorophyll a Light-Harvesting Complex from Trachydiscus minutus Seki, Soichiro; Cupellini, Lorenzo; Bína, David; Betti, Elena; Urajová, Petra; Tanaka, Hideaki; Miyata, Tomoko; Namba, Keiichi; Kurisu, Genji; Polívka, Tomáš; Litvín, Radek; Fujii, Ritsuko Photosynthetic organisms employ light-harvesting complexes (LHCs) to optimize energy capture under variable light conditions. The freshwater eustigmatophyte Trachydiscus minutus accumulates a red-shifted violaxanthin–chlorophyll protein (rVCP) that contributes to far-red light harvesting using only chlorophyll (Chl) a molecules, without chemical modification or substitution of pigments. Based on high-resolution cryo-EM and multiscale quantum chemical calculations, we uncovered a heterodimer-based tetrameric architecture, representing a unique oligomerization mode among LHCs. Within each heterodimer, Chls a are distinctively arranged adjacent to the terminal emitter, forming an unprecedentedly extended chlorophyll cluster. Quantum chemical calculations reveal three strong exciton-coupled pigment domains, two of which reside in the large cluster and solely account for the intense far-red absorption near 700 nm without contributions from charge–transfer states. Our structural and quantum chemical characterizations of far-red light harvesting reveal a molecular mechanism of red spectral tuning that relies on protein-controlled excitonic coupling of identical Chl a pigments, as demonstrated here in this eustigmatophyte, highlighting diverse adaptations for harvesting spectrally shifted, low-energy light. Sat, 13 Dec 2025 00:00:00 GMT https://dspace.jcu.cz/handle/20.500.14390/47550 2025-12-13T00:00:00Z https://dspace.jcu.cz/handle/20.500.14390/47548 Amblyostatin-1, the first salivary cystatin with host immunomodulatory and anti-inflammatory properties from the Neotropical tick Amblyomma sculptum, vector of Brazilian spotted fever Molari, Wilson Santos; Jmel, Mohamed Amine; Assis, Josiane Betim; Frazão-Silva, Alan; Bernardi, Julia Moura; Huamanrayme, Gretta; Medina, José María; Esteves, Eliane; Antão, Solange Cristina; Costa, Gabriel Cerqueira Alves; Tanaka, Aparecida Sadae; Fogaca, Andréa Cristina; Franta, Zdenek; Tirloni, Lucas; Kotsyfakis, Michalis; Sá-Nunes, Anderson Introduction: The Neotropical tick Amblyomma sculptum is the primary vector of Rickettsia rickettsii, the causative agent of Brazilian spotted fever, a disease associated with high fatality rates. Tick saliva, a complex mixture of bioactive molecules essential for successful blood feeding, facilitates pathogen transmission and modulates host immune responses. A comprehensive evaluation of the salivary gland transcriptome database reveals that protease inhibitors are abundantly expressed molecules in tick saliva during feeding. Thus, this study aims to describe and characterize the most expressed member of the cystatin family identified in Amblyomma sculptum salivary transcriptome, named Amblyostatin-1. Methods: Bioinformatic tools were employed for in silico analysis of the Amblyostatin-1 sequence and structure. A recombinant version of Amblyostatin-1 was expressed in an Escherichia coli system, evaluated against a panel of cysteine proteases in biochemical assays, and used to generate antibodies in immunized mice. The biological activities of Amblyostatin-1 were assessed by its effects on dendritic cell maturation in vitro and in a carrageenaninduced inflammation model in vivo. Results: Based on its sequence and predicted three-dimensional structure, Amblyostatin-1 is classified as an I25B cystatin, and its recombinant form selectively inhibits cathepsins L, C, and S at different rates, with a low nanomolar Ki value of 0.697 ± 0.22 nM against cathepsin L. Regarding its biological activities, recombinant Amblyostatin-1 partially affects LPS-induced dendritic cell maturation by downmodulating the costimulatory molecules CD80 and CD86 at higher micromolar concentrations (3 μM) while promoting IL-10 production at nanomolar concentrations (100 nM). The apparent lack of Amblyostatin-1-specific antibody responses in immunized mice suggests an impairment of antigen processing and presentation in vivo. Furthermore, in a carrageenan-induced inflammation model, Amblyostatin-1 decreased edema formation and neutrophil infiltration into the skin without affecting other myeloid cells. Discussion: These findings establish Amblyostatin-1 as a novel salivary cystatin with immunomodulatory and anti-inflammatory properties, highlighting its potential as an immunobiological agent. Thu, 17 Jul 2025 00:00:00 GMT https://dspace.jcu.cz/handle/20.500.14390/47548 2025-07-17T00:00:00Z