Figure 6.

Conserved residue N441 is required for NIS targeting to the plasma membrane. A) Sequence alignment of IL-6 of SLC5A family members. The N441 position in NIS and corresponding residues in other members are indicated in blue. Left and right shaded sequences represent fragments of TMS XI and XII, respectively, according to the crystal structure of vSGLT. B) Steady-state I⁻ uptake in nontransfected (Nt) or transiently transfected COS-7 cells expressing WT, N441Q, or N441A NIS. Cells were incubated with 20 μM I⁻ in the absence (dark bars) or presence (light bars) of 80 μM ClO₄⁻. Results are expressed as means ± sd (pmol I⁻/μg DNA). Values are representative of ≥3 different experiments; in each experiment activity was analyzed in triplicate. C) Representative FACS histograms showing NIS expression under permeabilized (top panel, total) and nonpermeabilized (bottom panel, surface) conditions. Cells were stained with anti-HA Ab, followed by R-phycoerythrin-conjugated anti-rat Ab. Nontransfected cells are represented in solid gray; WT NIS, blue line; N441Q NIS, red line; and N441A NIS, green line.