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Transcobalamin receptor CD320, responsible for vitamin B12 cellular uptake, is present on the cell surface as a homo-oligomer
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DOI：10.1016/j.jbc.2026.113286.png)
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Abstract
En 中文
CD320, also known as the transcobalamin receptor, is a key receptor that mediates the cellular uptake of circulating vitamin B12 bound to transcobalamin. In humans, CD320 abnormalities cause metabolic and neurological disorders. Previous biochemical studies indicate that the CD320 is a monomeric receptor. In this study, we conducted molecular and cellular experiments in human embryonic kidney 293 cells to examine biosynthesis and molecular forms of human CD320. We found that CD320 was present on the cell surface in an oligomeric form, which consisted of five homomers interconnected via disulfide bonds, possibly in one or both low-density lipoprotein receptor (LDLR)-like domains. Deletion of the LDLR-like domains prevented CD320 oligomerization and cell surface localization, thereby impairing cellular uptake of vitamin B12. By analyzing biochemical forms of CD320 in intracellular compartments, we showed that CD320 oligomerization occurred in the endoplasmic reticulum (ER) and that this process required the transmembrane domain but not N- or O-glycosylation of CD320. Moreover, we showed that the CD320 ΔE88 variant, identified in infants with abnormal vitamin B12 metabolism, did not prevent CD320 oligomerization but delayed CD320 trafficking out of the ER, resulting in low levels of CD320 oligomers on the cell surface. Together, our findings provide important insights into the biochemical nature and cellular mechanisms underlying the function of CD320 and associated pathologies in vitamin B12 metabolism.
Keywords:
CD320
cell surface receptor
cobalamin
oligomerization
vitamin B12 metabolism
ATP1A1
Na+/K+ ATPase 1
Ben-gal
benzyl N-acetyl-α-D-galactosaminide
BFA
brefeldin A
CB
Coomassie blue
CHX
cycloheximide
DMEM
Dulbecco’s modified Eagle’s medium
DMSO
dimethylsulfoxide
EGF
epidermal growth factor
ER
endoplasmic reticulum
FBS
fetal bovine serum
GAPDH
glyceraldehyde-3-phosphate dehydrogenase
HEK293
human embryonic kidney 293
holo-TC
holo-transcobalamin
HRP
horseradish peroxidase
LC-MS
liquid chromatography-mass spectrometry
LDLR
low-density lipoprotein receptor
NR
non-reducing
OR
O-glycan-rich
PBS
phosphate buffered saline
PS
Ponceau S
R
reducing
TM
transmembrane
WT
wild type
Journal
IF:
3.9
Papers:
11.2W
Citations:
28.3W
Organization
Cited Papers