TRPA1 is an ion channel and has been proposed as a thermosensor across species. In invertebrate and ancestral vertebrates such as fly, mosquito, frog, lizard and snakes, TRPA1 serves as a heat receptor, a sensory input utilized for heat avoidance or infrared detection. However, in mammals, whether TRPA1 is a receptor for noxious cold is highly controversial, as channel activation by cold was observed by some groups but disputed by others. Here we attribute the discrepancy to species differences. We show that cold activates rat and mouse TRPA1 but not human or rhesus monkey TRPA1. At the molecular level, a single residue within the S5 transmembrane domain (G878 in rodent but V875 in primate) accounts for the observed difference in cold sensitivity. This residue difference also underlies the species-specific effects of menthol. Together, our findings identify the species-specific cold activation of TRPA1 and reveal a molecular determinant of cold-sensitive gating.

The pituitary adenylate cyclase-activating polypeptide (PACAP) receptor is a class II G protein-coupled receptor that contributes to many different cellular functions including neurotransmission, neuronal survival, and synaptic plasticity. The solution structure of the potent antagonist PACAP (residues 6-38) complexed to the N-terminal extracellular (EC) domain of the human splice variant hPAC1-R-short (hPAC1-RS) was determined by NMR. The PACAP peptide adopts a helical conformation when bound to hPAC1-RS with a bend at residue A18 and makes extensive hydrophobic and electrostatic interactions along the exposed ␤-sheet and interconnecting loops of the N-terminal EC domain. Mutagenesis data on both the peptide and the receptor delineate the critical interactions between the C terminus of the peptide and the C terminus of the EC domain that define the high affinity and specificity of hormone binding to hPAC1-RS. These results present a structural basis for hPAC1-RS selectivity for PACAP versus the vasoactive intestinal peptide and also differentiate PACAP residues involved in binding to the N-terminal extracellular domain versus other parts of the full-length hPAC1-RS receptor. The structural, mutational, and binding data are consistent with a model for peptide binding in which the C terminus of the peptide hormone interacts almost exclusively with the N-terminal EC domain, whereas the central region makes contacts to both the N-terminal and other extracellular parts of the receptor, ultimately positioning the N terminus of the peptide to contact the transmembrane region and result in receptor activation.NMR ͉ vasoactive intestinal peptide ͉ G protein-coupled receptor S even transmembrane domain G protein-coupled receptors (GPCRs) are cell surface proteins that transduce signals initiated by hormones or neurotransmitters into the cell (1). Class II GPCRs are a family of receptors that bind structurally related peptide hormones including glucagon, glucagon-like peptides, vasoactive intestinal peptide (VIP), corticotrophinreleasing factor (CRF), parathyroid hormone (PTH), and pituitary adenylate cyclase-activating polypeptide (PACAP) hormone. This family of receptors is capable of regulating intracellular concentrations of cAMP through activation of the adenylate cyclase pathway, and some can also modulate intracellular calcium levels through the phospholipase C pathway. Structurally, they have low homology with other GPCR families but are well conserved within the family. They all contain a relatively large amino-terminal extracellular (EC) domain that plays a critical role in ligand binding. The N-terminal EC hormone-binding domains have common features, typically containing six conserved cysteine residues, two conserved tryptophan residues, and an aspartate residue which has been suggested to be critical for ligand binding (2, 3). Many of the peptide ligands of these receptors have related sequences and can bind to more than one receptor subtype (4).VIP and PACAP are two prototypical neuropeptides that modulate C...

As a member of the transient receptor potential (TRP) ion channel superfamily, the ligand-gated ion channel TRPA1 has been implicated in nociceptive function and pain states. The endogenous ligands that activate TRPA1 remain unknown. However, various agonists have been identified, including environmental irritants (e.g., acrolein) and ingredients of pungent natural products [e.g., allyl isothiocyanate (ITC), cinnamaldehyde, allicin, and gingerol]. In general, these agents are either highly reactive, nonselective, or not potent or efficacious, significantly limiting their utilities in the study of TRPA1 channel properties and biological functions. In a search for novel TRPA1 agonists, we identified 3Ј-carbamoylbiphenyl-3-yl cyclohexylcarbamate (URB597), a potent and systemically active inhibitor of fatty acid amide hydrolase (FAAH). This enzyme is responsible for anandamide degradation and therefore has been pursued as an antinociceptive and antiepileptic drug target. Using Ca 2ϩ influx assays and patch-clamp techniques, we demonstrated that URB597 could activate heterologously expressed human and rat TRPA1 channels, whereas two other FAAH inhibitors (i.e., URB532 and Compound 7) had no effect. When applied to inside-out membrane patches expressing rat TRPA1, URB597 elicited single-channel activities with a unitary conductance of 40 pS. Furthermore, URB597 activated TRPA1 channels endogenously expressed in a population of rat dorsal root ganglion neurons that also responded to ITC. In contrast to its effect on TRPA1, URB597 inhibited TRPM8 and had no effects on TRPV1 or TRPV4. Thus, we conclude that URB597 is a novel agonist of TRPA1 and probably activates the channel through a direct gating mechanism.TRPA1, also known as ANKTM1 and p120, belongs to the transient receptor potential (TRP) superfamily, which consists of a large group of cation channels present in species ranging from yeast to mammals (Montell et al., 2002;Clapham, 2003). In mammals, more than 20 TRP channels have been discovered, playing critical roles in physiological processes ranging from vasorelaxation, fertility, and cell growth to sensory function. Mammalian TRP channels can be divided into TRPC, TRPV, TRPM, TRPML, TRPP, and TRPA subfamilies. TRPA1 is the only member of the TRPA subfamily and is restrictively expressed in sensory neurons of dorsal root ganglia, trigeminal ganglia, and hair cells of the inner ear (Jaquemar et al., 1999;Story et al., 2003;Corey et al., 2004;Bautista et al., 2005;Nagata et al., 2005;Obata et al., 2005). In dorsal root ganglia (DRG) or trigeminal ganglia, it is specifically colocalized with TRPV1, CGRP and the bradykinin receptors. The TRPA1 channel was shown to be activated by cold stimuli with a temperature threshold of 17°C, which approximates the pain-inducing threshold of noxious cold

Apolipoprotein E is a 299-residue lipid carrier protein produced in both the liver and the brain. The protein has three major isoforms denoted apoE2, apoE3, and apoE4 which differ at positions 112 and 158 and which occur at different frequencies in the human population. Genome-wide association studies indicate that the possession of two apoE4 alleles is a strong genetic risk factor for late-onset Alzheimer’s disease (LOAD). In an attempt to identify a small molecule stabilizer of apoE4 function that may have utility as a therapy for Alzheimer’s disease, we carried out an NMR-based fragment screen on the N-terminal domain of apoE4 and identified a benzyl amidine based fragment binder. In addition to NMR, binding was characterized using various other biophysical techniques, and a crystal structure of the bound core was obtained. Core elaboration ultimately yielded a compound that showed activity in an IL-6 and IL-8 cytokine release assay.