Biology subjects

Henderson, P.

Publications and source records attributed to Henderson, P..

3 recordsLinked to original sources

bioRxiv2026

A bacterial Rhesus transporter retunes a structurally conserved ammonium pore into a reversible nitrogen valve

How conserved proteins acquire new physiological functions is a central question in molecular evolution. Rather than inventing new architectures, evolution often repurposes existing scaffolds, preserving core structural features while retuning the molecular logic that connects mechanism to physiology. Membrane transporters offer a powerful test of this principle because substrate selectivity, directionality, flux and energetic cost must be coordinated at the interface between the cell and its environment. The Amt/Mep/Rh superfamily controls one of the most fundamental requirements of cellular life: the movement of reduced nitrogen across biological membranes. Despite sharing a highly conserved ammonium-conducting pore, these proteins support distinct physiological roles, including nitrogen acquisition, sensing and homeostatic control. Here, we combined targeted mutagenesis, electrophysiology, yeast complementation and molecular dynamics simulations to define the transport logic of NeRh50, a bacterial Rhesus protein from the ammonia-oxidising bacterium Nitrosomonas europaea. We show that NeRh50 is not simply an AmtB-like ammonium importer. Instead, it uses the conserved Amt/Mep/Rh pore as a branched transport system in which inward uptake and export-linked transport can be separated genetically and mechanistically. Two conserved pore residues define this division of labour. A residue at the external entrance couples ammonium recruitment to productive inward uptake, whereas a second residue deeper in the pore enables a distinct transport mode required for substrate release when intracellular nitrogen accumulates. Thus, conserved Amt/Mep/Rh pore landmarks do not impose a single mechanism. Their local chemistry can be reassigned to generate different transport outputs, allowing NeRh50 to function as a reversible nitrogen valve. These findings reveal how minimal retuning within an ancient membrane-protein scaffold can rewire transport directionality and adapt nitrogen handling to ecological and physiological demand.

biochemistry↗

bioRxiv2026

Lipid-associated architecture and divergent ammonium transport distinguish a bacterial Rhesus protein

Nitrification is a major process in the global nitrogen cycle, initiated by the oxidation of ammonia to nitrite. The ammonia-oxidising bacterium Nitrosomonas europaea catalyses this first and rate-limiting step and depends on ammonium both as an energy substrate and as a nitrogen source, making ammonium acquisition central to its physiology. Cellular ammonium transport is mediated by the Amt/Mep/Rh superfamily, whose members share a conserved fold despite divergent physiological roles. Remarkably, N. europaea lacks a canonical prokaryotic Amt transporter and instead expresses NeRh50, a Rh-family protein proposed to have been acquired from a eukaryotic lineage. Here, we determine a cryo-EM structure of NeRh50 that reveals tightly associated lipids at the monomer-monomer interfaces, including density consistent with an unusual inverted lipid orientation. Native mass spectrometry and molecular dynamics simulations further support persistent lipid association at these interfaces. NeRh50 also differs functionally from canonical AmtB, selectively mediating electrogenic ammonium transport with ~70-fold lower apparent affinity. Transport is enhanced under alkaline conditions but not by an imposed proton gradient, suggesting membrane-potential dependence. Together, these findings reveal divergence from canonical Amt proteins in both membrane-associated architecture and transport properties, providing insight into the functional and evolutionary diversification of the Amt/Mep/Rh superfamily.

biochemistry↗

bioRxiv2026

Maternal-fetal immune conflict contributes to male-specific impairments in a mouse model of neurodevelopmental disorders

Autism spectrum disorder (ASD) arises from genetic and environmental risk factors. One environmental factor, maternal immune activation (MIA)--in which pathogenic infection during pregnancy increases ASD risk in offspring--disproportionately affects males. However, the basis for this male-specific vulnerability, and the mechanisms by which inflammatory signals cross the maternal-fetal interface to affect the male embryo, remain largely unknown. Using the poly(I:C) mouse model of neurodevelopmental disorders, we characterize fetal, placental, and amniotic changes occurring within twenty-four hours of MIA. We find that 30% of embryos exhibit large-scale teratogenic abnormalities--ranging from decreased fetal weight to altered sensory organ development--while 70% develop normally. These abnormalities occur exclusively in a subset of males, never in females. Single-nucleus transcriptomics revealed robust induction of pro-inflammatory gene programs in the placentas of affected males across a broad range of cell types, and most prominently in spongiotrophoblasts--fetally derived cells that partly form the maternal-fetal border. These cells simultaneously down-regulate extracellular matrix and hormone biosynthesis pathways, coinciding with a breakdown in placental structural integrity and the accumulation of immune cells and cytokines in the amniotic fluid. One such cytokine, IL-6, is required for MIA-evoked developmental abnormalities to emerge. Our data indicate that MIA drives a rapid shift from an immunosuppressive to a pro-inflammatory maternal-fetal interface in a vulnerable subset of male embryos, producing acute, sex-restricted developmental deficits. We propose that male embryos may express unique proteins capable of triggering this inflammatory response, which--combined with MIA-induced loss of maternal immunosuppression--selectively derails male embryonic development.

developmental biology↗