An apical Phe-His pair defines the Orai1-coupling site and its occlusion within STIM1.

Ca2+ signal-generation through inter-membrane junctional coupling between endoplasmic reticulum (ER) STIM proteins and plasma membrane (PM) Orai channels, remains a vital but undefined mechanism. We identify two unusual overlapping Phe-His aromatic pairs within the STIM1 apical helix, one of which (F394-H398) mediates important control over Orai1-STIM1 coupling. In resting STIM1, this locus is deeply clamped within the folded STIM1-CC1 helices, likely near to the ER surface. The clamped environment in holo-STIM1 is critical-positive charge replacing Phe-394 constitutively unclamps STIM1, mimicking store-depletion, negative charge irreversibly locks the clamped-state. In store-activated, unclamped STIM1, Phe-394 mediates binding to the Orai1 channel, but His-398 is indispensable for transducing STIM1-binding into Orai1 channel-gating, and is spatially aligned with Phe-394 in the exposed Sα2 helical apex. Thus, the Phe-His locus traverses between ER and PM surfaces and is decisive in the two critical STIM1 functions-unclamping to activate STIM1, and conformational-coupling to gate the Orai1 channel.

Cold sensory transduction through the STIM-Orai signaling pathway.

The STIM-Orai signaling pathway mediates Ca2+ signals vital for controlling transcription and cell growth. The Ca2+ sensing STIM proteins are activated by depletion of Ca2+ stored in the ER, and translocate into ER-PM junctions to gate PM Orai channels. STIM1 activation also results from heating STIM1 proteins, and new evidence reveals the STIM1-mediated gating of Orai1 channels is activated by noxious cooling of cells. This activation of the STIM-Orai pathway may be important in mediating vascular dilation that occurs in response to severe cold exposure.

Unidentified Branches of the Posterior Femoral Cutaneous Nerve and Persistent Neuropathy.

The posterior femoral cutaneous nerve (PFCN) is an extensive nerve with numerous collateral branches which provide cutaneous innervation to 2/3rds of the posterior thigh, the infragluteal fold, as well as the lateral anal region, scrotum, and labia majora through its inferior cluneal and pudendal nerve branches. It has been noted in multiple studies that patients can experience persistent PFCN neuropathy after surgery for decompression of known collateral branches. In this study, we used 17 formaldehyde (7 male and 10 female) perfused cadavers obtained from Hershey Medical Center's donor program to study the branching patterns of the PFCN. As a result, we found that 41% of individuals have an unidentified proximal branch of PFCN that recurs over the inferolateral border of the gluteus maximus, suggesting other areas of potential compression or nerve entrapment that could lead to persistent PFCN neuropathy that's not improved after treatment for sciatic, pudendal, or inferior cluneal neuralgia. We hope these findings allow clinicians to modify current surgical techniques and improve patients' post-operative quality of life.

Orai channel C-terminal peptides are key modulators of STIM-Orai coupling and calcium signal generation.

Junctional coupling between endoplasmic reticulum (ER) Ca2+-sensor STIM proteins and plasma membrane (PM) Orai channels mediates Ca2+ signals in most cells. We reveal that PM-tethered, fluorescently tagged C-terminal M4x (fourth transmembrane helix contains a cytoplasmic C-terminal extension) peptides from Orai channels undergo a Leu-specific signature of direct interaction with the STIM1 Orai-activating region (SOAR), exactly mimicking STIM1 binding to gate Orai channels. The 20-amino-acid Orai3-M4x peptide associates avidly with STIM1 within ER-PM junctions, functions to competitively block native Ca2+ signals, and mediates a key modification of STIM-Orai coupling induced by 2-aminoethoxydiphenyl borate. By blocking STIM-Orai coupling, the Orai3-M4x peptide reveals the critical role of Orai channels in driving Ca2+ oscillatory signals and transcriptional control through NFAT. The M4x peptides interact independently with SOAR dimers consistent with unimolecular coupling between Orai subunits and STIM1 dimers. We reveal the critical role of M4x helices in defining the coupling interface between STIM and Orai proteins to mediate store-operated Ca2+ signals.

Internal Neurolysis of the Common Peroneal Nerve With Lower Extremity Flexion Increases Likelihood for Direct End-End Nerve Repairs.

Introduction An understanding of common peroneal neuropathy is essential to improving current surgical techniques and overcoming limitations of permanent common peroneal nerve (CPN) damage, which negatively impacts quality of life. This study focuses on quantifying additional nerve length after CPN internal neurolysis with varying degrees of lower extremity flexion, in order to improve end-end nerve repairs in the setting of injury with a significant gap. Materials and methods Full and partial neurolysis dissections were performed on salt- and formaldehyde-perfused cadavers. For accurate measurement of additional length obtained, all dissections were palpated at the fibular head and CPNs transected proximally at the distal fascial border. We chose this site to measure the nerve length obtained because it is the common site for CPN injury and the most clinically applicable. The amount of nerve length gained from neurolysis alone was measured at the location of the common peroneal nerve passing deep to peroneus longus before and after being transected. Nerve length after neurolysis was measured in cm at 10° increments, using a protractor starting at 90° and ending at 0°. Results Both formaldehyde- and salt-perfused cadavers have a significant difference in nerve length obtained after neurolysis at each angle of measurement. This is seen for both dissection groups with p-values <0.05. Conclusions In this study, we found a direct statistically significant relationship between extent of neurolysis and increased angle of measurement, to amount of addition nerve length obtained in both neurolysis groups despite fixation type.