Identification
of N-linked glycosylation sites in hTfR2. (A) Schematic
representation of the N-linked glycosylation sites on hTfR2 protein
sequence. Asn 240, 339, 540, and 754 are predicted to be glycosylated
(underlined). Asn 554 (bold) has an NPS/T motif and was used as a
negative control because this Asn could not be glycosylated. (B) Western
blot analysis of cell lysates from HEK 293 cells transiently transfected
with empty vector (pcDNA3, Con) or hTfR2-FLAG expression vectors encoding
either the wild type (WT) or N-glycosylation site mutants (N240A,
N339A, N540A, and N754A). Positions 240, 339, and 754 are identified
as being glycosylated, but position 540 is not. N554A was used as
a negative control. (C) Western blot analysis of cell lysates from
HEK 293 cells transiently transfected with empty vector (pcDNA3, Con),
WT hTfR2 (WT), the hTfR2 nonglycosylated triple mutant (N240/339/754A,
3-Mut), or the quadruple mutant (N240/339/540/754A, 4-Mut). (D) HEK
293 cells transfected with empty vector (pcDNA3, Con), WT hTfR2 (WT),
or the hTfR2 nonglycosylated mutant (N240/339/754A, 3-Mut) were harvested,
and cell lysates were incubated with or without PNGase F before Western
blotting. The samples were electrophoresed on a 12 cm 10% polyacrylamide
gel for 24 h to ensure greater separation, transferred to nitrocellulose,
and probed with anti-Flag antibody for TfR2. The data represent three
independent experiments.