Biology subjects

Minor, D. L.

Publications and source records attributed to Minor, D. L..

13 recordsLinked to original sources

bioRxiv2026

Saxiphilin is a broad-spectrum toxin sponge for C13-modified saxitoxins

Saxitoxin (STX) and its congeners (paralytic shellfish toxins, PSTs) are among the most potent small-molecule toxins. PSTs are produced by harmful algal blooms and derive toxicity by disrupting voltage-gated sodium channel (NaV) bioelectrical signaling. Understanding how PST structural variation affects target binding is crucial to develop means to counteract PSTs and exploit these natural products as drug development leads. Frog and toad saxiphilins (Sxphs) are soluble, high-affinity STX toxin sponge proteins that offer a powerful platform to define PST-protein interactions. Here, we show that American bullfrog (Rana catesbeiana) RcSxph and High Himalaya frog (Nanorana parkeri) NpSxph bind a broad set of C13-modified STX congeners. High-resolution X-ray crystal structures of toxin complexes with RcSxph, RcSxph mutants, and NpSxph unveil two C13-aryl congener binding modes, termed compact and open, that depend on the RcSxph Tyr558 local environment. These results highlight a remarkable adaptability of Sxphs for accommodating chemically diverse STX analogs and reveal unexpected toxin conformational plasticity. These findings have implications for understanding PST interactions with biological targets and informing design of STX-based probes and NaV modulators.

biophysics↗

bioRxiv2025

Saxiphilin functions as a "toxin sponge" protein that counteracts the effects of saxitoxin poisoning

Saxitoxin (STX) is among the most potent toxins known, is classified as a chemical weapon, and is the archetype of the paralytic shellfish toxin (PST) family produced by marine and freshwater harmful algal blooms (HAB)1-3. STX causes paralysis and death through inhibition of voltage-gated sodium channels (NaVs), has no antidote, and poses a public health and commercial fishing threat due to its accumulation in seafood and increasing HAB occurrences1,4. Although STX is lethal to varied vertebrates5-7, including humans4,8,9, certain frogs resist STX poisoning6,7. This phenotype is thought to depend on soluble toxin sponge high-affinity STX binding proteins (saxiphilins, Sxphs)6,7,10,11 that provide resistance through a competition mechanism different from classic target site ion channel mutation mechanisms12-14. Here, we test this idea directly and show that a single dose of American bullfrog (Rana catesbeiana) Sxph (RcSxph) is sufficient to counteract STX neurotoxicity and lethality in mice using paradigms where STX and Sxph are administered together or sequentially in either order. Importantly, this function requires the RcSxph high-affinity STX binding site. Our findings provide in vivo validation that Sxphs are toxin sponges that protect against STX poisoning and highlight the potential to harness this protein class as antidotes for PSTs and other toxins.

pharmacology and toxicology↗

bioRxiv2025

A lipid plug affects K2P6.1(TWIK-2) function

Lipids are integral to ion channel function yet delineating mechanisms by which they affect function remains challenging. Within the K2P family of leak potassium channels1-3, observation of tubular densities interpreted as alkyl chains occupying lateral fenestrations linking the pore and bilayer4-8 raised the possibility that lipid access from the bilayer acts as a regulatory mechanism4-7. Here, we present cryo-electron microscopy (cryo-EM) structures of the human leak potassium channel K2P6.1 (TWIK2)9-11 and mutants in nanodisc and detergent environments that reveal an unusual conformation in the first selectivity filter (SF1) and a pair of two-chain lipids within the channel cavity (denoted the lipid plug). The chains of each plug lipid occupy separate binding sites that laterally extend to the bilayer from the channel cavity. One, the upper leg, matches the previously identified alkyl chain binding site4-8,12. The second, the lower leg, occupies a fenestration common with K2P1.1 (TWIK1)13. Together, they demonstrate a bidentate means to coordinate each plug lipid that offers a reinterpretation of previous observations. Structures of a K2P6.1 (TWIK2) mutant that directs the channel to the plasma membrane14 and an R257A mutant that increases function yield plugged and unplugged forms. Notably, the R257A plugged form shows a change in lipid plug position, indicating a key role for this residue in lipid binding. Together, our data suggest that occupation of the central cavity by the lipid plug serves as a mechanism to render the TWIK channels inactive and points to the importance of lipid plug removal to create an ion permeable pore. Such a mechanism could provide a potent way for limiting the leak function of K2Ps based on cellular location or other contextual factors.

biophysics↗

bioRxiv2024

Structural basis for saxitoxin congener binding and neutralization by anuran saxiphilins

Dinoflagellates and cyanobacteria in harmful red tide algal blooms produce saxitoxin (STX) and [~]50 congeners that block voltage-gated sodium channel (NaV) function and disrupt bioelectrical signals1-4. Consuming seafood carrying these lethal toxins causes paralytic shellfish poisoning (PSP), a growing public health hazard due to climate change5-7 that motivates efforts to detect these toxins and counteract their noxious effects. Although structural studies of NaVs8,9 and anuran soluble STX binding proteins known as saxiphilins (Sxphs)10,11 revealed convergent binding modes for the bis-guanidinium STX core10,11, the structural basis for STX congener recognition is unknown. Here, we show that American bullfrog (Rana catesbeiana) RcSxph10,11 and High Himalaya frog (Nanorana parkeri) NpSxph10 use a pre-organized pocket to sequester STX congeners through a binding mode shared with STX. This lock and key recognition yields a tradeoff between a relatively rigid high-affinity toxin binding site in which bound waters are crucial and the ability of Sxphs to accommodate STX congener modifications. Importantly, functional studies show that Sxphs act as toxin sponges that reverse NaV block by multiple STX congeners and can detect these bis-guanidinium toxins in a radioligand receptor binding assay (RBA) for PSP toxin environmental testing12,13. Our findings establish how Sxphs sequester diverse neurotoxins and reveal structural factors underlying STX congener binding differences between Sxphs and NaVs that are rooted in the distinct toxin binding orientations on these two targets. These insights expand the molecular foundation required for understanding toxin sponge action and for guiding development of new means to monitor PSTs and mitigate their harmful effects.

biophysics↗

bioRxiv2024

Structure of the human K2P13.1(THIK-1) channel reveals a novel hydrophilic pore restriction and lipid cofactor site

The halothane-inhibited K2P leak potassium channel K2P13.1 (THIK-1)1-3 is found in diverse cells1,4 including neurons1,5 and microglia6-8 where it affects surveillance6, synaptic pruning7, phagocytosis7, and inflammasome-mediated interleukin-1{beta} release6,8,9. As with many K2Ps1,5,10-14 and other voltage-gated ion channel (VGIC) superfamily members3,15,16, polyunsaturated fatty acid (PUFA) lipids modulate K2P13.1 (THIK-1)1,5,14,17 via a poorly understood mechanism. Here, we present cryo-electronmicroscopy (cryo-EM) structures of human K2P13.1 (THIK-1) and mutants in lipid nanodiscs and detergent. These reveal that, unlike other K2Ps13,18-24, K2P13.1 (THIK-1) has a two-chamber aqueous inner cavity obstructed by a M4 transmembrane helix tyrosine (Tyr273, the flow restrictor). This hydrophilic barrier can be opened by an activatory mutation, S136P25, at natural break in the M2 transmembrane helix and by intrinsic channel dynamics. The structures also reveal a buried lipid in the P1/M4 intersubunit interface at a location, the PUFA site, that coincides with the TREK subfamily K2P modulator pocket for small molecule agonists18,26,27. This overlap, together with the effects of mutation on K2P13.1 (THIK-1) PUFA responses, indicates that the PUFA site lipids are K2P13.1 (THIK-1) cofactors. Comparison with the PUFA-responsive VGIC Kv7.1 (KCNQ1)28-31 reveals a shared role for the equivalent pore domain intersubunit interface in lipid modulation, providing a framework for dissecting the effects of PUFAs on the VGIC superfamily. Our findings reveal the unique architecture underlying K2P13.1 (THIK-1) function, highlight the importance of the P1/M4 interface in control of K2Ps by both natural and synthetic agents, and should aid development of THIK subfamily modulators for diseases such as neuroinflammation6,32 and autism6.

biophysics↗

bioRxiv2023

Development of covalent chemogenetic K2P channel activators

K2P potassium channels regulate excitability by affecting cellular resting membrane potential in the brain, cardiovascular system, immune cells, and sensory organs. Despite their important roles in anesthesia, arrhythmia, pain, hypertension, sleep, and migraine, the ability to control K2P function remains limited. Here, we describe a chemogenetic strategy termed CATKLAMP (Covalent Activation of TREK family K+ channels to cLAmp Membrane Potential) that leverages the discovery of a site in the K2P modulator pocket that reacts with electrophile-bearing derivatives of a TREK subfamily small molecule activator, ML335, to activate the channel irreversibly. We show that the CATKLAMP strategy can be used to probe fundamental aspects of K2P function, as a switch to silence neuronal firing, and is applicable to all TREK subfamily members. Together, our findings exemplify a new means to alter K2P channel activity that should facilitate studies both molecular and systems level studies of K2P function and enable the search for new K2P modulators.

biophysics↗

bioRxiv2022

Structural basis for CaVα2δ:gabapentin binding

Gabapentinoid drugs for pain and anxiety act on the CaV2{delta}-1 and CaV2{delta}-2 subunits of high-voltage activated calcium channels (CaV1s and CaV2s). Here, we present the cryo-EM structure of the gabapentin-bound brain and cardiac CaV1.2/CaV{beta}3/CaV2{delta}-1 channel. The data reveal a binding pocket in the CaV2{delta}-1 dCache1 domain that completely encapsulates gabapentin and define CaV2{delta} isoform sequence variations that explain gabapentin binding selectivity of CaV2{delta}-1 and CaV2{delta}-2.

biophysics↗

bioRxiv2022

EMC holdase:CaV1.2/CaVβ3 complex and CaV1.2 channel structures reveal CaV assembly and drug binding mechanisms

Voltage-gated ion channels (VGICs) comprise multiple structural units whose assembly is required for function1,2. There is scant structural understanding of how VGIC subunits assemble and whether chaperone proteins are required. High-voltage activated calcium channels (CaVs)3,4 are paradigmatic multi-subunit VGICs from electrically excitable tissues whose function and trafficking is powerfully shaped by interactions between pore-forming CaV1 or CaV2 CaV13 and auxiliary CaV{beta}5, and CaV2{delta} subunits6,7. Here, we present cryo-EM structures of human brain and cardiac CaV1.2 bound with CaV{beta}3 to a chaperone, the endoplasmic reticulum membrane protein complex (EMC)8,9, and of the isolated CaV1.2/CaV{beta}3/CaV2{delta}-1 channel. These provide an unprecedented view of an EMC holdase:client complex and define EMC sites, the TM and Cyto docks, whose interaction with the client channel cause partial extraction of a pore subunit and splay open the CaV2{delta} interaction site. The structures further identify the CaV2{delta} binding site for gabapentinoid anti-pain and anti-anxiety drugs6, show that EMC and CaV2{delta} channel interactions are mutually exclusive, and indicate that EMC to CaV2{delta} handoff involves a Ca2+-dependent step and ordering of multiple CaV1.2 elements. Together, the structures unveil a CaV assembly intermediate and previously unknown EMC client binding sites that have broad implications for biogenesis of VGICs and other membrane proteins.

biophysics↗

bioRxiv2022

Definition of a saxitoxin (STX) binding code enables discovery and characterization of the Anuran saxiphilin family

American bullfrog (Rana castesbeiana) saxiphilin (RcSxph) is a high-affinity toxin sponge protein thought to prevent intoxication by saxitoxin (STX), a lethal bis-guanidinium neurotoxin that causes paralytic shellfish poisoning (PSP) by blocking voltage-gated sodium channels (NaVs). How specific RcSxph interactions contribute to STX binding has not been defined and whether other organisms have similar proteins is unclear. Here, we use mutagenesis, ligand binding, and structural studies to define the energetic basis of Sxph:STX recognition. The resultant STX recognition code enabled engineering of RcSxph to improve its ability to rescue NaVs from STX and facilitated discovery of ten new frog and toad Sxphs. Definition of the STX binding code and Sxph family expansion among diverse Anurans separated by [~]140 million years of evolution provides a molecular basis for understanding the roles of toxin sponge proteins in toxin resistance and for developing novel proteins to sense or neutralize STX and related PSP toxins. TeaserA conserved STX recognition motif from frog and toad saxiphilins defines molecular principles of paralytic toxin binding.

biophysics↗

bioRxiv2021

Quaternary structure independent folding of voltage-gated ion channel pore domain subunits

Every voltage-gated ion channel (VGIC) superfamily member has an ion conducting pore consisting of four pore domain (PD) subunits that are each built from a common plan comprising an antiparallel transmembrane helix pair, a short, obliquely positioned helix (the pore helix), and selectivity filter. The extent to which this structure, the VGIC-PD fold, relies on the extensive quaternary interactions observed in PD assemblies is unclear. Here, we present crystal structures of three bacterial voltage-gated sodium channel (BacNaO_SCPLOWVC_SCPLOW) pores that adopt a surprising set of non-canonical quaternary structures and yet maintain the native tertiary structure of the PD monomer. This context-independent structural robustness demonstrates that the VGIC-PD fold, the fundamental VGIC structural building block, can adopt its native-like tertiary fold independent of native quaternary interactions. In line with this observation, we find that the VGIC-PD fold is not only present throughout the VGIC superfamily and other channel classes but has homologs in diverse transmembrane and soluble proteins. Characterization of the structures of two synthetic Fabs (sFabs) that recognize the VGIC-PD fold shows that such sFabs can bind purified full-length channels and indicates that non-canonical quaternary PD assemblies can occur in the context of complete VGICs. Together, our data demonstrate that the VGIC-PD structure can fold independently of higher-order assembly interactions and suggest that full-length VGIC PDs can access previously unknown non-canonical quaternary states. These PD properties have deep implications for understanding how the complex quaternary architectures of VGIC superfamily members are achieved and point to possible evolutionary origins of this fundamental VGIC structural element.

biophysics↗

bioRxiv2020

Sodium channel toxin-resistance mutations do not govern batrachotoxin (BTX) autoresistance in poison birds and frogs

Poisonous organisms carry small molecule toxins that alter voltage-gated sodium channel (Na{checkmark}) function. Among these, batrachotoxin (BTX) from Pitohui toxic birds and Phyllobates poison frogs, stands out because of its lethality and unusual effects on Nav function. How these toxin-bearing organisms avoid autointoxication remains poorly understood. In poison frogs, a Nav DIVS6 pore-forming helix N[->]T mutation has been proposed as the BTX resistance mechanism. Here, we show that this variant is absent from Pitohui and poison frog Navs, incurs a strong cost that compromises channel function, and fails to produce BTX-resistant channels when tested in the context of poison frog Navs. We further show that captive-raised poison frogs are BTX resistant, even though they bear BTX-sensitive Navs. Hence, our data refute the hypothesis that BTX autoresistance is rooted in Nav mutations and instead suggest that more generalizable mechanisms such as toxin sequestration act to protect BTX-bearing species from autointoxication.

biophysics↗

bioRxiv2020

K2P channel C-type gating involves asymmetric selectivity filter order-disorder transitions

K2P channels regulate nervous, cardiovascular, and immune system functions1,2 through the action of their selectivity filter (C-type) gate3-6. Although structural studies show K2P conformations that impact activity7-13, no selectivity filter conformational changes have been observed. Here, combining K2P2.1 (TREK-1) X-ray crystallography in different potassium concentrations, potassium anomalous scattering, molecular dynamics, and functional studies, we uncover the unprecedented, asymmetric, potassium-dependent conformational changes underlying K2P C-type gating. Low potassium concentrations evoke conformational changes in selectivity filter strand 1 (SF1), selectivity filter strand 2 (SF2), and the SF2-transmembrane helix 4 loop (SF2-M4 loop) that destroy the S1 and S2 ion binding sites and are suppressed by C-type gate activator ML335. Shortening the uniquely long SF2-M4 loop to match the canonical length found in other potassium channels or disrupting the conserved Glu234 hydrogen bond network supporting this loop blunts C-type gate response to various physical and chemical stimuli. Glu234 network destabilization also compromises ion selectivity, but can be reversed by channel activation, indicating that the ion binding site loss reduces selectivity similar to other channels14. Together, our data establish that C-type gating occurs through potassium-dependent order-disorder transitions in the selectivity filter and adjacent loops that respond to gating cues relayed through the SF2-M4 loop. These findings underscore the potential for targeting the SF2-M4 loop for the development of new, selective K2P channel modulators.

biophysics↗

bioRxiv2019

Polynuclear ruthenium amines inhibit K2P channels via a 'finger in the dam' mechanism

The trinuclear ruthenium amine Ruthenium Red (RuR) inhibits diverse ion channels including K2P potassium channels, TRPs, the mitochondrial calcium uniporter, CALHMs, ryanodine receptors, and Piezos. Despite this extraordinary array, there is very limited information for how RuR engages its targets. Here, using X-ray crystallographic and electrophysiological studies of an RuR-sensitive K2P, K2P2.1 (TREK-1) I110D, we show that RuR acts by binding an acidic residue pair comprising the Keystone inhibitor site under the K2P CAP domain archway above the channel pore. We further establish that Ru360, a dinuclear ruthenium amine not known to affect K2Ps, inhibits RuR-sensitive K2Ps using the same mechanism. Structural knowledge enabled a generalizable RuR super-responder design strategy for creating K2Ps having nanomolar sensitivity. Together, the data define a finger in the dam inhibition mechanism acting at a novel K2P inhibitor binding site. These findings highlight the polysite nature of K2P pharmacology and provide a new framework for K2P inhibitor development.

biophysics↗