Zinc binding to a conserved motif in STIM1 induces clustering and SOCE activation

STIM1 is a key regulator of calcium homeostasis in the endoplasmic reticulum (ER), activated upon ER calcium depletion through calcium dissociation from its EF-hand domain. While much is known about its domain organization and activation-induced structural rearrangements, certain regulatory mechanisms remain unclear. A short conserved region upstream of the EF-hand has been previously implicated in redox modulation of STIM1, but its exact function was unknown.

We used a combination of biochemical assays, mutagenesis, and imaging approaches to investigate the structural and functional role of this conserved region. Zinc binding was assessed by spectroscopy, and STIM1 clustering was monitored by fluorescence microscopy. Statistical analyses were applied where appropriate to evaluate significance.

We demonstrate that this conserved segment coordinates zinc ions and is essential for STIM1 activation. Zinc binding to this region enhances STIM1 clustering, a prerequisite for Orai-mediated calcium influx. Mutations disrupting zinc coordination impaired clustering and downstream calcium signaling.

Our results identify a zinc-binding module upstream of the EF-hand as a critical determinant of STIM1 activation. These findings provide new insights into the molecular interplay between zinc and calcium signaling and suggest a regulatory mechanism by which cellular zinc levels may influence ER calcium homeostasis.