The functions of G-protein coupled receptors (GPCRs) are primarily mediated and modulated by three families of proteins: the heterotrimeric G proteins, the G-protein coupled receptor kinases (GRKs), and the arrestins1. G proteins mediate activation of second messenger-generating enzymes and other effectors, GRKs phosphorylate activated receptors2, and arrestins subsequently bind phosphorylated receptors and cause receptor desensitization3. Arrestins activated by interaction with phosphorylated receptors can also mediate G protein-independent signaling by serving as adaptors to link receptors to numerous signaling pathways4. Despite their central role in regulation and signaling of GPCRs, a structural understanding of β-arrestin activation and interaction with GPCRs is still lacking. Here, we report the crystal structure of β-arrestin1 in complex with a fully phosphorylated 29 amino acid carboxy-terminal peptide derived from the V2 vasopressin receptor (V2Rpp). This peptide has previously been shown to functionally and conformationally activate β-arrestin15. To capture this active conformation, we utilized a conformationally-selective synthetic antibody fragment (Fab30) that recognizes the phosphopeptide-activated state of β-arrestin1. The structure of the β-arrestin1:V2Rpp:Fab30 complex shows striking conformational differences in β-arrestin1 compared to its inactive conformation. These include rotation of the amino and carboxy-terminal domains relative to each other, and a major reorientation of the “lariat loop” implicated in maintaining the inactive state of β-arrestin1. These results reveal, for the first time at high resolution, a receptor-interacting interface on β-arrestin, and they suggest a potentially general molecular mechanism for activation of these multifunctional signaling and regulatory proteins.

KcsA is a proton-activated, voltage-modulated K ؉ channel that has served as the archetype pore domain in the Kv channel superfamily. Here, we have used synthetic antigen-binding fragments (Fabs) as crystallographic chaperones to determine the structure of full-length KcsA at 3.8 Å, as well as that of its isolated C-terminal domain at 2.6 Å. The structure of the full-length KcsA-Fab complex reveals a well-defined, 4-helix bundle that projects Ϸ70 Å toward the cytoplasm. This bundle promotes a Ϸ15°bending in the inner bundle gate, tightening its diameter and shifting the narrowest point 2 turns of helix below. Functional analysis of the full-length KcsA-Fab complex suggests that the C-terminal bundle remains whole during gating. We suggest that this structure likely represents the physiologically relevant closed conformation of KcsA.

Detection and adaptation to cold temperature is crucial to survival. Cold sensing in the innocuous range of cold (>10-15°C) in the mammalian peripheral nervous system is thought to rely primarily on transient receptor potential (TRP) ion channels, most notably the menthol receptor, TRPM8. Here we report that TRP cation channel, subfamily C member 5 (TRPC5), but not TRPC1/TRPC5 heteromeric channels, are highly cold sensitive in the temperature range 37-25°C. We found that TRPC5 is present in mouse and human sensory neurons of dorsal root ganglia, a substantial number of peripheral nerves including intraepithelial endings, and in the dorsal lamina of the spinal cord that receives sensory input from the skin, consistent with a potential TRPC5 function as an innocuous cold transducer in nociceptive and thermosensory nerve endings. Although deletion of TRPC5 in 129S1/SvImJ mice resulted in no temperature-sensitive behavioral changes, TRPM8 and/or other menthol-sensitive channels appear to underpin a much larger component of noxious cold sensing after TRPC5 deletion and a shift in mechanosensitive C-fiber subtypes. These findings demonstrate that highly cold-sensitive TRPC5 channels are a molecular component for detection and regional adaptation to cold temperatures in the peripheral nervous system that is distinct from noxious cold sensing.pain | single-fiber | thermo-transient receptor potential | nociception | temperature sensing N ociceptors and thermoreceptive neurons, such as cold and heat receptors, innervate the skin and deep tissues. The cell bodies of sensory nerve endings are clustered in ganglia located in the vertebral column and cranium. Their projections extend to the skin where they arborize in terminals embedded between keratinocytes. Although nociceptors are polymodal and respond to stimuli (cold, heat, pressure, and noxious chemicals) that are capable of producing tissue damage and pain (1), cold receptors are unimodal and specialized to detect cool and cold temperatures (2). Transient receptor potential (TRP) ion channels are principal transducers of thermal stimuli that depolarize nerve terminals to the action potential threshold. Action potentials then relay the sensory information to integrative centers in the spinal cord and brain.All proteins are temperature sensitive, but most ion channels exhibit two-to threefold increases in gating with a 10°C change in temperature (Q 10 = 2-3). Certain ion channels exhibit dramatic temperature sensitivity in gating over physiologically relevant ranges (Q 10 = 10-30). Mammalian ion channels with such high Q 10 values include particular two-pore K + channels (3), the voltage-gated proton channel (4), transient receptor potential cation channel subfamily V members 1-3 (TRPV1-3) (5-7), transient receptor potential menthol receptor 8 (TRPM8) (8), and in some reports, TRP cation channel subfamily A member 1 (TRPA1) (9, 10). There is no a priori requirement for cold encoding by high Q 10 channels-action potential firing rates are affected perforce by temperature,...

Immediately placed ITI TE implant leads to initial intraosseous stability and interface mechanical properties comparable with a wide diameter implant.

A set of phage display sorting strategies and validation methodologies are presented that are capable of producing high performance synthetic antibodies (sABs) with customized properties. Exquisite control of antigen and conditions during the phage display selection process can yield sABs that: 1) recognize conformational states, 2) target specific regions of the surface of a protein, 3) induce conformational changes, and 4) capture and stabilize multiprotein complexes. These unique capabilities open myriad opportunities to study complex macromolecular processes inaccessible to traditional affinity reagent technology. We present detailed protocols for de novo isolation of binders, as well as examples of downstream biophysical characterization. The methods described are generalizable and can be adapted to other in vitro direct evolution approaches based on yeast or mRNA display.