{
 "paper": "kolb-2026-igabasnfr2",
 "model": "supplied:runs/kolb-2026-igabasnfr2/plain-claim.answer.json",
 "prompt": "extract/prompts/plain-claim.md",
 "claims": [
  {
   "slug": "alt-signal-from-cross-reactivity",
   "role": "hypothesis",
   "panel": "",
   "plain": "The fluorescence attributed to iGABASnFR2 comes from compounds that resemble GABA rather than from GABA itself."
  },
  {
   "slug": "crystal-structure-pdb-9d57",
   "role": "methodological",
   "panel": "fig3 (or structural supplement)",
   "plain": "The crystal structure of iGABASnFR2, showing its binding pocket and cpGFP arrangement, is deposited in the Protein Data Bank."
  },
  {
   "slug": "hypothesis-improved-sensor-enables-new-biology",
   "role": "hypothesis",
   "panel": "hypothesis",
   "plain": "A sufficiently sensitive GABA sensor enables measurements iGABASnFR1 cannot make at all, rather than cleaner versions of old ones."
  },
  {
   "slug": "hypothesis-saturation-mutagenesis-yields-improved-sensor",
   "role": "hypothesis",
   "panel": "hypothesis",
   "plain": "Mutating a handful of residues around iGABASnFR1's GABA-binding pocket and cpGFP linkers yields a far better sensor without losing selectivity."
  },
  {
   "slug": "igabasnfr2-13fold-expression-increase",
   "role": "empirical",
   "panel": "fig1C",
   "plain": "iGABASnFR2 produces about thirteen times as many responding pixels as iGABASnFR1, reflecting better sensitivity and better membrane trafficking."
  },
  {
   "slug": "igabasnfr2-2p-compatible",
   "role": "methodological",
   "panel": "fig4e, fig4f, fig4-supplement3",
   "plain": "iGABASnFR2 works under two-photon imaging, and both new variants are less sensitive to pH than iGABASnFR1."
  },
  {
   "slug": "igabasnfr2-cpgfp-rigid-on-gaba-binding",
   "role": "interpretation",
   "panel": "fig3a",
   "plain": "GABA binding closes iGABASnFR2's binding lobes but leaves the fluorescent cpGFP domain almost unmoved, unlike GCaMP with calcium."
  },
  {
   "slug": "igabasnfr2-fourfold-sensitivity-gain",
   "role": "empirical",
   "panel": "fig1, fig2",
   "plain": "iGABASnFR2 gives a roughly fourfold larger fluorescence change than iGABASnFR1 for the same stimulation in cultured neurons."
  },
  {
   "slug": "igabasnfr2-gaba-selective-specificity",
   "role": "control",
   "panel": "fig4-supplement1, fig4-supplement2",
   "plain": "iGABASnFR2 responds to GABA and not to structurally similar compounds, none of which block or distort its GABA response."
  },
  {
   "slug": "igabasnfr2-invivo-barrel-cortex",
   "role": "empirical",
   "panel": "fig6c, fig6-video1",
   "plain": "iGABASnFR2 detects GABA spilling into the extracellular space of mouse barrel cortex when the whiskers are stimulated."
  },
  {
   "slug": "igabasnfr2-kinetics-rise-decay",
   "role": "empirical",
   "panel": "fig2c, fig2d",
   "plain": "iGABASnFR2 rises faster and decays more slowly than iGABASnFR1, while the negative-going variant rises more slowly than both."
  },
  {
   "slug": "igabasnfr2-oncell-affinity-sevenfold",
   "role": "empirical",
   "panel": "fig4b",
   "plain": "On the neuron surface iGABASnFR2 binds GABA about seven times more tightly than iGABASnFR1, still above resting GABA levels."
  },
  {
   "slug": "igabasnfr2-retina-direction-selectivity",
   "role": "empirical",
   "panel": "fig5",
   "plain": "iGABASnFR2 shows that starburst amacrine cells release GABA differently depending on motion direction, which iGABASnFR1 could not resolve."
  },
  {
   "slug": "igabasnfr2-single-bouton-hippocampus",
   "role": "empirical",
   "panel": "fig6a, fig6b",
   "plain": "iGABASnFR2 detects GABA released from single hippocampal interneuron boutons, where iGABASnFR1 gave no signal at all."
  },
  {
   "slug": "igabasnfr2-single-exponential-kinetics",
   "role": "empirical",
   "panel": "fig4c, fig4d",
   "plain": "iGABASnFR2 and its negative-going variant bind GABA in one fast step, while iGABASnFR1 binds in two slower phases."
  },
  {
   "slug": "igabasnfr2n-negative-going-variant",
   "role": "empirical",
   "panel": "fig1C, fig1D",
   "plain": "A variant called iGABASnFR2n dims rather than brightens when GABA binds, and is also far better expressed than iGABASnFR1."
  },
  {
   "slug": "mutagenesis-3947-variants-screened",
   "role": "methodological",
   "panel": "fig1B, fig1C",
   "plain": "A screen of nearly 4,000 variants at 39 sites yielded 93 more responsive than iGABASnFR1 and 22 better in both response and expression."
  },
  {
   "slug": "prediction-improved-sensor-enables-new-measurements",
   "role": "prediction",
   "panel": "prediction",
   "plain": "iGABASnFR2 should beat iGABASnFR1 at single boutons, at single-trial direction selectivity in retina, and at whisker-evoked GABA in the living brain."
  },
  {
   "slug": "prediction-screen-yields-multiple-improved-variants",
   "role": "prediction",
   "panel": "prediction",
   "plain": "The screen should yield several variants beating iGABASnFR1 on response, at least one also better expressed, and some behaving in new ways."
  },
  {
   "slug": "scope-sensor-engineering-paper",
   "role": "scope",
   "panel": "scope",
   "plain": "All tests use cultured neurons, purified protein, retina, hippocampal slice and mouse cortex, not awake or non-mammalian preparations."
  },
  {
   "slug": "screening-scope-wet-lab-only",
   "role": "scope",
   "panel": "all figures (assessment)",
   "plain": "The performance claims rest on bench measurements that cannot be reproduced from the deposited code and data, which only redraw the figures."
  }
 ]
}