A Novel Role for the Amino Terminus of the Ryanodine Receptor, a Ca Release Channel, as the Retention Signal to the Endoplasmic Reticulum

Abstract

The ryanodine receptor (RyR) is an intracellular calcium ion (Ca²⁺ ) release channel. The C-terminal region of RyR was proposed to contain the transmembrane segments that form the channel into the endoplasmic reticulum (ER) while the large N-terminus, termed the “foot”, was thought to be the cytoplasmic region of the protein. In order to confirm this proposed structure of RyR1, we have generated RyR1 mutants that were serially deleted from the 3' to the 5' terminal which were tagged to enhanced green fluorescent protein (EGFP) in Chinese hamster ovary (CHO) cells. The C-terminal deleted clones which lacked a putative transmembrane region and a small N-terminal portion which was further deleted to the N-terminal Thr184 were retained in the cytoplasmic region even after being permeablized by absolute methanol, the same as full-length RyR1. These results suggest that there are also sequences for ER retention within the N-terminal region (between Met1 to Thr184) of RyR1.