Biology subjects

Hibbs, R. E.

Publications and source records attributed to Hibbs, R. E..

5 recordsLinked to original sources

bioRxiv2025

A sensory system for mating in octopus

Sensory systems for mate recognition maintain species boundaries and influence diversification. Therefore, uncovering how molecules and receptors evolve to mediate this critical function is essential to understanding biodiversity. Male octopuses use a specialized arm called the hectocotylus to identify females and navigate their internal organs to reach the oviduct and deliver sperm. Here, we discovered that the hectocotylus is a dual sensory and mating organ that uses contactdependent chemosensation of progesterone, a conserved ovarian hormone. We identify chemotactile receptors for progesterone and resolve the structural basis for their evolution from ancestral neurotransmitter receptors and subsequent expansion and tuning across cephalopods. These findings reveal principles by which sensory innovations shape reproductive behavior and suggest mechanisms for how sensory evolution contributes to the diversification of life.

cell biology↗

bioRxiv2025

Shape-Shifting Conotoxins Reveal Divergent Pore-Targeting Mechanisms in Nicotinic Receptors

The neuronal 7 nicotinic acetylcholine receptor (7-nAChR) and muscle-type nicotinic acetylcholine receptor (mt-nAChR) are pivotal in synaptic signaling within the brain and the neuromuscular junction respectively. Additionally, they are both targets of a wide range of drugs and toxins. Here, we utilize cryoEM to delineate structures of these nAChRs in complex with the conotoxins ImI and ImII from Conus imperialis. Despite nominal sequence divergence, ImI and ImII exhibit discrete binding preferences and adopt drastically different conformational states upon binding. ImI engages the orthosteric sites of the 7-nAChR, while ImII forms distinct pore-bound complexes with both the 7-nAChR and mt-nAChR. Strikingly, ImII adopts a compact globular conformation that binds as a monomer to the 7-nAChR pore and as an oblate dimer to the mt-nAChR pore. These structural characterizations advance our understanding of nAChR-ligand interactions as well as the subtle sequence variations that result in dramatically altered functional outcomes in small peptide toxins. Importantly, these results further elucidate the broad nature of cone snail toxin activities and highlight how targeted molecular evolution can give rise to functionally similar activities with surprisingly diverse mechanisms of action.

neuroscience↗

bioRxiv2025

Environmental microbiomes drive chemotactile sensation in octopus

Microbial communities coat nearly every surface in the environment and have co-existed with animals throughout evolution. Whether animals exploit omnipresent microbial cues to navigate their surroundings is not well understood. Octopuses use "taste by touch" chemotactile receptors (CRs) to explore the seafloor, but how they distinguish meaningful surfaces from the rocks and crevices they encounter is unknown. Here, we report that secreted signals from microbiomes of ecologically relevant surfaces activate CRs to guide octopus behavior. Distinct molecules isolated from specific bacterial strains located on prey or eggs bind single CRs in subtly different structural conformations to elicit distinct mechanisms of receptor activation, ion permeation and signal transduction, and maternal care and predation behavior. Thus, microbiomes on ecological surfaces act at the level of primary sensory receptors to inform behavior. Our study demonstrates that uncovering interkingdom interactions is essential to understanding how animal sensory systems evolved in a microbe rich world. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/641191v1_ufig1.gif" ALT="Figure 1"> View larger version (140K): org.highwire.dtl.DTLVardef@15f365eorg.highwire.dtl.DTLVardef@1ea5606org.highwire.dtl.DTLVardef@1b5ad1aorg.highwire.dtl.DTLVardef@779e6e_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIChemotactile receptors (CRs) detect microbiomes of prey and progeny C_LIO_LIDiverse microbial signals bind single CRs with distinct structural conformations C_LIO_LIDistinct microbial signals activate single CRs to permeate different ions C_LIO_LIEnvironmental microbes elicit octopus predatory and maternal behaviors C_LI

physiology↗

bioRxiv2024

Autoimmune mechanisms elucidated through muscle acetylcholine receptor structures

Skeletal muscle contraction is mediated by acetylcholine (ACh) binding to its ionotropic receptors (AChRs) at neuromuscular junctions. In myasthenia gravis (MG), autoantibodies target AChRs, disrupting neurotransmission and causing muscle weakness. Despite available treatments, patient responses vary, suggesting pathogenic heterogeneity. Current information on molecular mechanisms of autoantibodies is limited due to the absence of structures of an intact human muscle AChR. Here, we overcome challenges in receptor purification and present high-resolution cryo-EM structures of the human adult AChR in different functional states. Using a panel of six MG patient-derived monoclonal antibodies, we mapped distinct epitopes involved in diverse pathogenic mechanisms, including receptor blockade, internalization, and complement activation. Electrophysiological and binding assays further defined how these autoantibodies impair AChR function. These findings provide critical insights into MG immunopathology, revealing previously unrecognized antibody epitope diversity and mechanisms of receptor inhibition, offering a foundation for personalized therapies targeting antibody-mediated autoimmune disorders. HighlightsO_LIHuman adult muscle AChR receptor structures in resting and desensitized states C_LIO_LIEpitope mapping for mechanistically distinct pathogenic MG autoantibodies C_LIO_LIStructural and functional elucidation of different inhibition mechanisms in MG C_LI

neuroscience↗

bioRxiv2022

Differential interactions of resting, activated, and desensitized states of the α7 nicotinic acetylcholine receptor with lipidic modulators

The 7 nicotinic acetylcholine receptor is a pentameric ligand-gated ion channel that modulates neuronal excitability, largely by allowing Ca2+ permeation. Agonist binding promotes transition from a resting state to an activated state, and then rapidly to a desensitized state. Recently, cryo-EM structures of the human 7 receptor in nanodiscs were reported in multiple conformations. These were selectively stabilized by inhibitory, activating, or potentiating compounds. However, the functional annotation of these structures, and their differential interactions with unresolved lipids and ligands, remain incomplete. Here, we characterized their ion permeation, membrane interactions, and ligand binding using computational electrophysiology, free-energy calculations, and coarse-grained molecular dynamics. In contrast to non-conductive structures in apparent resting and desensitized states, the structure determined in the presence of the potentiator PNU-120596 was consistent with an activated state permeable to Ca2+. Transition to this state was associated with compression and rearrangement of the membrane, particularly in the vicinity of the peripheral MX helix. An intersubunit transmembrane site was implicated in selective binding of either PNU-120596 in the activated state, or cholesterol in the desensitized state. This substantiates functional assignment of all three lipid-embedded 7-receptor structures with ion permeation simulations. It also proposes testable models of their state-dependent interactions with lipophilic ligands, including a mechanism for allosteric modulation at the transmembrane subunit interface.

biophysics↗