Autor/es:
PARODER, V; NICOLA, JP; GINTER, CS; CARRASCO, N
Resumen:
a(+)/I(-) symporter (NIS)-mediated active accumulation of I(-) in
thyrocytes is a key step in the biosynthesis of the iodine-containing
thyroid hormones T3 and T4. Several NIS mutants have been identified as a
cause of congenital I(-) transport defect (ITD), and their
investigation has yielded valuable mechanistic information on NIS. Here
we report novel findings derived from the thorough characterization of
the ITD-causing mutation R124H, located in the second intracellular loop
(IL-2). R124H NIS is incompletely glycosylated and colocalizes with
endoplasmic reticulum (ER)-resident protein markers. As a result, R124H
NIS is not targeted to the plasma membrane and therefore does not
mediate any I(-) transport in transfected COS-7 cells. Strikingly,
however, the mutant is intrinsically active, as revealed by its ability
to mediate I(-) transport in membrane vesicles. Of all the amino acid
substitutions we carried out at position 124 (K, D, E, A, W, N and Q),