Table 1.

Subunit compositions and functions of oligosaccharyltransferase (OST).

OST Subunits	Type of OST	Functions in OST Complexes	Phenotypes Caused by Mutations	Phenotypes Caused by Downregulation	References
STT3A	STT3A-OST	Catalytic subunit, co-translational glycosylation	STT3A-CDG	Impaired co-translational glycosylation	[42]
STT3B	STT3B-OST	Catalytic subunit, post-translational glycosylation	STT3B-CDG	Impaired post-translational glycosylation	[42]
RPN1	Shared	Binding to ribosome	Not known	Reduced expression of STT3A and STT3B	[23,35]
RPN2	Shared	Binding to ribosome?	Not known	Hypoglycosylation of P-glycoprotein and CD63	[44,45,46]
TMEM258	Shared	Association with RPN1	Not known	Increased intestinal inflammation in dextran sodium sulfate-treated haploinsufficient mice	[26]
DAD1	Shared	Stabilization of RPN1, RPN2 and OST48	Increased susceptibility to apoptotic cell death at non-permissive temperature	Reduced expression of STT3A, STT3B, OST48/DDOST and KCP2	[47,48,49]
OST48/DDOST	Shared	Stabilization of STT3A-OST and STT3B-OST	DDOST-CDG	Reduced expression of STT3A, STT3B, DAD1 and KCP2	[49,50]
OST4	Shared	Stabilization of STT3A-OST, but not STT3B-OST	Not known	Hypoglycosylation of prosaposin and reduced expression of STT3A and KCP2	[27]
DC2/OSTC and KCP2	STT3A-OST	Association with the Sec61 protein-conducting channel, co-translational glycosylation	Not known	Impaired co-translational glycosylation	[28,35]
TUSC3	STT3B-OST	Thioredoxin, glycosylation at Cys-proximal sites	Autosomal recessive mental retardation	Impaired Mg2+ uptake and tumor progression	[33,51,52,53,54,55,56,57,58,59,60,61,62,63,64]
MAGT1	STT3B-OST	Thioredoxin, glycosylation at Cys-proximal sites	X-linked immunodeficiency	Impaired Mg2+ uptake	[33,52,65,66]