Biology subjects

Abettan, A.

Publications and source records attributed to Abettan, A..

4 recordsLinked to original sources

bioRxiv2026

Conformational dynamics of ND2 antiporter-like subunit in intact and truncated complex I

Respiratory complex I is a large redox-driven proton pump and contributes to the proton motive force required for ATP generation in mitochondria and bacteria. It has been extensively studied with structural and biochemical approaches leading to enhanced understanding of its three- dimensional architecture. Despite significant progress in deciphering its catalytic function, the redox-coupled proton pumping mechanism remains unclear and extensively debated. The three membrane-bound antiporter-like subunits ND2, ND4 and ND5 are responsible for pumping protons from the negatively charged side (N-side) of the membrane to the positively charged side (P-side). Emerging evidence supports the role of ND5 subunit in releasing pumped protons to the P-side of the membrane, but the question whether ND2 and ND4 also contribute to proton release remains unanswered. Here, we performed atomistic molecular dynamics (MD) simulations of an intact and a truncated model of complex I in which ND5 and ND4 subunits are removed in-silico. The simulation data reveals a previously unobserved conformational change in the P-side region of ND2 subunit that occurs much more easily in a truncated model of complex I, as also estimated based on free energy calculations. The conformational change, in part triggered by the artificial exposure of ND2 subunit to lipid bilayer, results in a local hydration of the region, similar to what has been observed in recent cryo-EM structure of plant CI:CIII2 supercomplex. We discuss the functional relevance of observed conformational transitions and identify residues that can be manipulated with biochemical approaches to shed light on proton pumping by complex I.

biophysics↗

bioRxiv2026

Gating Mechanism of the Human Connexin 45 Gap Junction Channel

Gap junction channels formed by the 21-member human connexin family enable direct intercellular exchange of ions and small signaling metabolites, coordinating electrical coupling across cardiac, neural and epithelial tissues. Connexin 45 (Cx45), encoded by GJC1, mediates impulse conduction in the atrioventricular node, His bundle, and Purkinje fibers, where disease-linked mutations cause progressive atrioventricular block and familial atrial fibrillation, yet no experimental structure has been reported, and its regulatory mechanism remains undefined. Here, we determine the structural basis of Cx45 gating and Ca2+ regulation using cryo-electron microscopy, mutational analysis, and molecular dynamics simulations. Cryo-EM structures of the apo (2.76 [A]), Ca2+-bound (2.65 [A]), and E41A mutant (3.55 [A]) channel reveal a neck constriction formed by Y45, establishing a steric gate distinct from other connexins. Ca2+ associates with E41, stabilizing the neck via electrostatic remodeling without global conformational change. Together, these data define a dual steric-electrostatic mechanism for Cx45 regulation and provide a structural framework for isoform-specific connexin gating relevant to cardiac physiology and conduction disease.

biochemistry↗

bioRxiv2025

Post-translational acylation drives folding and activity of the CyaA bacterial toxin.

Post-translational modifications critically shape protein conformation and function, yet how they regulate bacterial toxins remains elusive. The adenylate cyclase (CyaA) toxin is a major virulence factor of Bordetella pertussis, the causative agent of whooping cough. CyaA is produced as an inactive precursor, proCyaA, which is activated by acylation of two lysine residues within the bacterium. Once acylated and secreted, CyaA invades innate immune cells and disrupts their phagocytic functions. High-resolution structural characterization of CyaA has remained elusive due to its size, multi-domain organization, flexibility, and aggregation propensity. Here, we overcome these challenges and generate the first structural ensembles of both non-acylated and acylated CyaA in solution by combining experimental data with integrative modeling. Coarse-grained molecular dynamics simulations reveal that acylation is critical to stabilize the native fold and to favorably orient CyaA on the target membrane. Overall, our findings reveal how post-translational acylation triggers native folding and provide mechanistic insights into the early steps of host cell intoxication.

biophysics↗

bioRxiv2025

In situ Structure of the Human Gap Junction

Gap junction plaques (GJPs) enable direct intercellular communication and consist of connexin channels arranged into two-dimensional lattices. While structures of purified connexin channels have informed models of gating, they omit key intracellular regions and lack native context. Here, we use cryogenic electron tomography and focused ion beam milling to determine the in situ structure of human connexin-43 (Cx43) GJPs in HEK293 cells at 14 [A] resolution. We discover a previously unresolved structural role for the large C-terminal domain in mediating lateral channel-channel interactions critical for plaque assembly. Coarse-grained molecular dynamics simulations reveal how lipids and cholesterol occupy the space between adjacent connexins. These findings resolve a decades-old question regarding gap junction organization and highlight a mechanistic function for the C-terminal domain, likely regulated by phosphorylation. Our study provides a structural blueprint for understanding how connexin diversity and regulation shape tissue-level communication in health and disease.

cell biology↗