Mechanistic insights into Orai dynamics during pore opening

Orai channels form highly Ca2+-selective pores in the plasma membrane (PM) and represent one of the two essential components of the Ca2+ release-activated Ca2+ (CRAC) channel. The second component is the Stromal Interaction Molecule (STIM) proteins, which is located in the endoplasmic reticulum (ER). Ca2+ influx through CRAC channels serves as the primary route of Ca2+ entry into the cell, playing a critical role in downstream signaling pathways such as gene transcription and cell proliferation. Activation of Orai channels is tightly coupled to the depletion of ER Ca2+ stores, which triggers STIM proteins to oligomerize and adopt an extended conformation that spans the ER-PM junction, enabling direct interaction with and activation of Orai. Several studies have shown that Orai activation is mediated by global conformational changes across the entire channel complex. In recent years, detailed functional analyses, structural investigations, genetic code expansion techniques, and molecular dynamics simulations have further refined our understanding of the molecular mechanisms underlying Orai1 pore opening and the associated amino acid-level conformational dynamics. In this review, we highlight proposed mechanisms, dynamic features, and functionally relevant contact sites across the Orai1 channel complex that contribute to gating and ion permeation, while also summarizing outstanding questions that remain to be resolved.