Biology subjects

McCullock, T. W.

Publications and source records attributed to McCullock, T. W..

4 recordsLinked to original sources

bioRxiv2024

Unique Pharmacology of mGluR homo- and heterodimers

Background and PurposeMetabotropic glutamate receptors (mGlus) are obligate dimer G protein coupled receptors that can all homodimerize and heterodimerize in select combinations. Responses of mGlu heterodimers to selective ligands, including orthosteric agonists and allosteric modulators, are largely unknown. Experimental ApproachThe pharmacological properties of each group II and III mGlu homodimer (except mGlu6) and several heterodimers were examined when stochastically assembled in HEK293T cells, or specifically measured using an improved G protein mediated BRET assay employing complimented fragments of NanoLuciferase. ResultsStochastically assembled receptors adopted unique signaling characteristics. Some favored the potency, efficacy or signaling kinetics of a dominant subunit, while others exhibited blended profiles reflective of a combination of homo- and heterodimers at various ratios of expressed receptor. Finally, group II and III mGlu dimers were examined for responses to selective agonists and allosteric modulators. Effects of glutamate and selective group II and III orthosteric agonists were found to result in unique concentration response profiles when examining each combination of group II and II mGlu. Effects of select allosteric modulators were examined for each mGlu2 containing dimer as well as several group III dimer pairs. Likewise, allosteric modulator effects were often unique across dimers containing the targeted subunit of the ligand being tested. ConclusionsResults demonstrate that mGlu dimers respond uniquely to selective ligands, and show that the mGlu family is not governed by generalizable rules dictating consequences of dimeric subunit interactions leading to signaling consequences.

pharmacology and toxicology↗

bioRxiv2023

Signaling specificity and kinetics of the human metabotropic glutamate receptors.

Metabotropic glutamate receptors (mGluRs) are obligate dimer G protein coupled receptors that can all function as homodimers. Here, each mGluR homodimer was examined for its G protein coupling profile using a BRET based assay that detects the interaction between a split YFP-tagged G{beta}1{gamma}2 and a Nanoluc tagged free G{beta}{gamma} sensor, MAS-GRK3-ct-NLuc with 14 specific G proteins heterologously expressed, representing each family. Canonically, the group II and III mGluRs (2&3, and 4, 6, 7&8, respectively) are thought to couple to Gi/o exclusively. In addition, the group I mGluRs (1&5) are known to couple to the Gq/11 family, and generally thought to also couple to the PTX-sensitive Gi/o family; some reports have suggested Gs coupling is possible as cAMP elevations have been noted. In this study, coupling was observed with all 8 mGluRs through the Gi/o proteins, and only mGluR1&5 through Gq/11, and perhaps surprisingly, not G14. None activated any Gs protein. Interestingly, coupling was seen with the group I and II, but not the group III mGluRs to G16. Slow but significant coupling to Gz was also seen with the group II receptors.

pharmacology and toxicology↗

bioRxiv2021

Topography and motion of the acid-sensing ion channel intracellular domains

Acid-sensing ion channels (ASICs) are trimeric cation-selective channels activated by decreases in extracellular pH. The intracellular N and C terminal tails of ASIC1 influence channel gating, trafficking, and signaling in ischemic cell death. Despite several x-ray and cryo-EM structures of the extracellular and transmembrane segments of ASIC1, these important intracellular tails remain unresolved. Here we describe the coarse topography of the cASIC1 intracellular domains determined by FRET, measured using either fluorescent lifetime imaging or patch clamp fluorometry. We find the C terminal tail projects into the cytosol by approximately 35 [A] and that the N and proximal segment of the C tail from the same subunits are closer than adjacent subunits. Using pH-insensitive fluorescent proteins, we fail to detect any relative movement between the N and C tails upon extracellular acidification but do observe axial motions of the membrane proximal segments towards the plasma membrane. Taken together, our study furnishes a coarse topographic map of the ASIC intracellular domains while providing directionality and context to intracellular conformational changes induced by extracellular acidification.

physiology↗

bioRxiv2019

Comparing the performance of mScarlet-I, mRuby3, and mCherry as FRET acceptors for mNeonGreen

Forster Resonance Energy Transfer (FRET) has become an immensely powerful tool to profile intra- and inter-molecular interactions. Through fusion of genetically encoded fluorescent proteins (FPs) researchers have been able to detect protein oligomerization, receptor activation, and protein translocation among other biophysical phenomena. Recently, two bright monomeric red fluorescent proteins, mRuby3 and mScarlet-I, have been developed. These proteins offer much improved physical properties compared to previous generations of monomeric red FPs that should help facilitate more general adoption of Green/Red FRET. Here we assess the ability of these two proteins, along with mCherry, to act as a FRET acceptor for the bright, monomeric, green-yellow FP mNeonGreen using intensiometric FRET and 2-photon Fluorescent Lifetime Imaging Microscopy (FLIM) FRET techniques. We first determined that mNeonGreen was a stable donor for 2-photon FLIM experiments under a variety of imaging conditions. We then tested the red FPs ability to act as FRET acceptors using mNeonGreen-Red FP tandem construct. With these constructs we found that mScarlet-I and mCherry are able to efficiently FRET with mNeonGreen in spectroscopic and FLIM FRET. In contrast, mNeonGreen and mRuby3 FRET with a much lower efficiency than predicted in these same assays. We explore possible explanations for this poor performance but are unable to definitively determine the cause, all though protein maturation seems to play a role. Overall, we find that mNeonGreen is an excellent FRET donor, and both mCherry and mScarlet-I, but not mRuby3, act as practical FRET acceptors, with mScarlet-I out performing mCherry due its higher brightness.

biophysics↗