Alternative translation initiation gives rise to two isoforms of orai1 with distinct plasma membrane mobilities

Advance Online Publication May 28, 2012 doi: 10.1242/?jcs.104919 Store-operated calcium entry is a nearly ubiquitous signaling pathway in eukaryotic cells. The plasma membrane store-operated channels are comprised of subunits of the recently discovered Orai proteins, the major one being Orai1.We have discovered that native Orai1 as well as expressed Orai1 exists in two forms in similar quantities: a longer form (Orai1a) of approximately 33 kDa, and a shorter form (Orai1ß) of approximately 23 kDa. The second Orai1ß form arises from alternative translation initiation from a methionine at position 64, and possibly also 71, in the longer, Orai1a form. In the sequence upstream of the initiation site of Orai1ß, there is a poly-arginine sequence previously suggested to be involved in interaction of Orai1 with plasma membrane phosphatidylinositol 4,5-bisphosphate. The loss of this phospholipid binding domain would be expected to influence the mobility of Orai1 protein in the plasma membrane. Indeed, experiments utilizing fluorescence recovery after photobleaching (FRAP) revealed that the recovery half-time for Orai1ß was significantly faster than for Orai1a. Since Orai1 must diffuse to sites of interaction with the Ca2+ sensor, STIM1, these two mobilities might provide for efficient recruitment of Orai1 subunits to sites of store-operated Ca2+ entry during agonist-induced Ca2+ signaling.

View the original article here

This post was made using the Auto Blogging Software from WebMagnates.org This line will not appear when posts are made after activating the software to full version.