Membrane Topography of Cardiac Triadin

Fusion constructs of partial sequences of triadin that contain green fluorescent protein at the N-terminus and glutathione transferase at the C-terminus have been expressed in human embryonic kidney −293 cells. A comparison of the subcellular disposition of a range of triadin fusion peptides indicates localization either to a few large organelles as a default target or to endoplasmic reticulum when amino acids 68–98 are present and structurally intact. Fluorescence from the conjugate of monochlorobimane with glutathione identifies whether the C-terminus has a cytoplasmic or luminal location. A stable transit of the membrane occurs in triadin2-98. Triadin2-117 and 2-267 give both cytoplasmic and luminal C-termini. Both triadin89-117 and triadin89-267 distribute in membranes, but do not cross them. The data are interpreted to indicate that cardiac triadin contains an α-helical membrane transit through the hydrophobic domain, 49–68, and a membrane association through the short hydrophobic domain, 102–114.