Bachelor of Science, Kutztown University Of Pennsylvania (2013)
PhD, Pennsylvania State University College of Medicine, Biomedical Sciences (2019)
Georgios Skiniotis, Postdoctoral Faculty Sponsor
An apical Phe-His pair defines the Orai1-coupling site and its occlusion within STIM1.
2023; 14 (1): 6921
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.
View details for DOI 10.1038/s41467-023-42254-x
View details for PubMedID 37903816
View details for PubMedCentralID PMC10616141
The tethered peptide activation mechanism of adhesion GPCRs.
Adhesion G-protein-coupled receptors (aGPCRs) are characterized by the presence of auto-proteolysing extracellular regions that are involved in cell-cell and cell-extracellular matrix interactions1. Self cleavage within the aGPCR auto-proteolysis-inducing (GAIN) domain produces two protomers-N-terminal and C-terminal fragments-that remain non-covalently attached after receptors reach the cell surface1. Upon dissociation of the N-terminal fragment, the C-terminus of the GAIN domain acts as a tethered agonist (TA) peptide to activate the seven-transmembrane domain with a mechanism that has been poorly understood2-5. Here we provide cryo-electron microscopy snapshots of two distinct members of the aGPCR family, GPR56 (also known as ADGRG1) and latrophilin3 (LPHN3 (also known as ADGRL3)). Low-resolution maps of the receptors in their N-terminal fragment-bound state indicate that the GAIN domain projects flexibly towards the extracellular space, keeping the encrypted TA peptide away from the seven-transmembrane domain. High-resolution structures of GPR56 and LPHN3 in their active, G-protein-coupled states, reveal that after dissociation of the extracellular region, the decrypted TA peptides engage the seven-transmembrane domain core with a notable conservation of interactions that also involve extracellular loop 2. TA binding stabilizes breaks in the middle of transmembrane helices 6 and 7 that facilitate aGPCR coupling and activation of heterotrimeric G proteins. Collectively, these results enable us to propose a general model for aGPCR activation.
View details for DOI 10.1038/s41586-022-04575-7
View details for PubMedID 35418682
The oxytocin signaling complex reveals a molecular switch for cation dependence.
Nature structural & molecular biology
Oxytocin (OT) and vasopressin (AVP) are conserved peptide signaling hormones that are critical for diverse processes including osmotic homeostasis, reproduction, lactation and social interaction. OT acts through the oxytocin receptor (OTR), a magnesium-dependent G protein-coupled receptor that is a therapeutic target for treatment of postpartum hemorrhage, dysfunctional labor and autism. However, the molecular mechanisms that underlie OTR activation by OT and the dependence on magnesium remain unknown. Here we present the wild-type active-state structure of human OTR bound to OT and miniGq/i determined by cryo-EM. The structure reveals a unique activation mechanism adopted by OTR involving both the formation of a Mg2+ coordination complex between OT and the receptor, and disruption of transmembrane helix 7 (TM7) by OT. Our functional assays demonstrate the role of TM7 disruption and provide the mechanism of full agonism by OT and partial agonism by OT analogs. Furthermore, we find that the identity of a single cation-coordinating residue across vasopressin family receptors determines whether the receptor is cation-dependent. Collectively, these results demonstrate how the Mg2+-dependent OTR is activated by OT, provide essential information for structure-based drug discovery efforts and shed light on the molecular determinants of cation dependence of vasopressin family receptors throughout the animal kingdom.
View details for DOI 10.1038/s41594-022-00728-4
View details for PubMedID 35241813
A key amino acid in STIM1 mediates coupling to gate the Orai1 channel
CELL PRESS. 2022: 374A
View details for Web of Science ID 000759523002373
G-protein activation by a metabotropic glutamate receptor.
Family C G-protein-coupled receptors (GPCRs) operate as obligate dimers with extracellular domains that recognize small ligands, leading to G-protein activation on the transmembrane (TM) domains of these receptors by an unknown mechanism1. Here we show structures of homodimers of the family C metabotropic glutamate receptor 2 (mGlu2) in distinct functional states and in complex with heterotrimeric Gi. Upon activation of the extracellular domain, the two transmembrane domains undergo extensive rearrangement in relative orientation to establish an asymmetric TM6-TM6 interface that promotes conformational changes in the cytoplasmic domain of one protomer. Nucleotide-bound Gi can be observed pre-coupled to inactive mGlu2, but its transition to the nucleotide-free form seems to depend on establishing the active-state TM6-TM6 interface. In contrast to family A and B GPCRs, G-protein coupling does not involve the cytoplasmic opening of TM6 but is facilitated through the coordination of intracellular loops 2 and 3, as well as a critical contribution from the C terminus of the receptor. The findings highlight the synergy of global and local conformational transitions to facilitate a new mode of G-protein activation.
View details for DOI 10.1038/s41586-021-03680-3
View details for PubMedID 34194039