Protein kinase Cs (PKCs) are a ubiquitous family of regulatory enzymes that associate with membranes and are activated by diacylglycerol or tumor-promoting agonists such as phorbol esters. The structure of the second activator-binding domain of PKC delta has been determined in complex with phorbol 13-acetate, which binds in a groove between two pulled-apart beta strands at the tip of the domain. The C3, C4, and C20 phorbol oxygens form hydrogen bonds with main-chain groups whose orientation is controlled by a set of highly conserved residues. Phorbol binding caps the groove and forms a contiguous hydrophobic surface covering one-third of the domain, explaining how the activator promotes insertion of PKC into membranes.

Vanilloid receptor 1 (TRPV1), a membrane-associated cation channel, is activated by the pungent vanilloid from chili peppers, capsaicin, and the ultra potent vanilloid from Euphorbia resinifera, resiniferatoxin (RTX), as well as by physical stimuli (heat and protons) and proposed endogenous ligands (anandamide, Narachidonyldopamine, N-oleoyldopamine, and products of lipoxygenase). Only limited information is available in TRPV1 on the residues that contribute to vanilloid activation. Interestingly, rabbits have been suggested to be insensitive to capsaicin and have been shown to lack detectable [ 3 H]RTX binding in membranes prepared from their dorsal root ganglia. We have cloned rabbit TRPV1 (oTRPV1) and report that it exhibits high homology to rat and human TRPV1. Like its mammalian orthologs, oTRPV1 is selectively expressed in sensory neurons and is sensitive to protons and heat activation but is 100-fold less sensitive to vanilloid activation than either rat or human. Here we identify key residues (Met 547 and Thr 550 ) in transmembrane regions 3 and 4 (TM3/4) of rat and human TRPV1 that confer vanilloid sensitivity, [ 3 H]RTX binding and competitive antagonist binding to rabbit TRPV1. We also show that these residues differentially affect ligand recognition as well as the assays of functional response versus ligand binding. Furthermore, these residues account for the reported pharmacological differences of RTX, PPAHV (phorbol 12-phenyl-acetate 13-acetate 20-homovanillate) and capsazepine between human and rat TRPV1. Based on our data we propose a model of the TM3/4 region of TRPV1 bound to capsaicin or RTX that may aid in the development of potent TRPV1 antagonists with utility in the treatment of sensory disorders.The receptor for capsaicin (a small vanilloid molecule extracted from "hot" chili peppers), designated vanilloid receptor 1 (also known as VR1 and TRPV1 1 (1)) has been cloned and shown to be a nonselective cation channel with high permeability to calcium. TRPV1 belongs to a superfamily of ion channels known as transient receptor potential channels (TRPs) several of which appear to be sensors of temperature (2, 3). TRPV1 can be activated by exogenous agonists (capsaicin and RTX) and by physical stimuli such as heat (Ͼ42°C) and protons (pH 5). Possible endogenous ligands released during tissue injury have also been suggested, including anandamide (arachidonylethanolamine or AEA) and products of lipoxygenases such as 12-hydroperoxyeicosatetraenoic acid, N-arachidonyldopamine (NADA), and N-oleoyldopamine (OLDA) (4 -7). Ji et al. (8) reported that TRPV1 is detectable at increased levels after inflammatory injury in rodents and speculated that the increased level of TRPV1 protein combined with the confluence of stimuli present in inflammatory injury states leads to a reduced threshold of activation of nociceptors that express TRPV1, i.e. hyperalgesia. Indeed the converse is true that TRPV1-deficient mice display reduced thermal hypersensitivity following inflammatory tissue injury (9). Structure-func...

The cloned vanilloid receptor VR1 has attracted recent attention as a molecular integrator of painful stimuli on primary sensory neurons. The existence of vanilloid-sensitive neurons in the brain is, however, controversial. In this study, we have used an antibody and a complementary RNA probe to explore the distribution of neurons that express VR1 in rat and in certain areas of human brain. In the rat, we observed VR1-expressing neurons throughout the whole neuroaxis, including all cortical areas (in layers 3 and 5), several members of the limbic system (e.g., hippocampus, central amygdala, and both medial and lateral habenula), striatum, hypothalamus, centromedian and paraventricular thalamic nuclei, substantia nigra, reticular formation, locus coeruleus, cerebellum, and inferior olive. VR1-immunopositive cells also were found in the third and fifth layers of human parietal cortex. Reverse transcription-PCR performed with rat VR1-specific primers verified the expression of VR1 mRNA in cortex, hippocampus, and hypothalamus. In the central nervous system, neonatal capsaicin treatment depleted VR1 mRNA from the spinal nucleus of the trigeminal nerve, but not from other areas such as the inferior olive. The finding that VR1 is expressed not only in primary sensory neurons but also in several brain nuclei is of great importance in that it places VRs in a much broader perspective than pain perception. VRs in the brain (and putative endogenous vanilloids) may be involved in the control of emotions, learning, and satiety, just to name a few exciting possibilities.