Creative Biostructure has developed custom MemPro™ gene-to-structure services for OST. OST is a membrane protein complex located in the endoplasmic reticulum (ER) membrane. As a glycosyltransferase, OST catalyzes the process of glycosylation. The most abundant of protein modifications in eukaryotes is asparagine (N)-linked glycosylation, which plays critical roles in cell functions, such as protein stability, intracellular trafficking and cell-cell interactions, etc. The proteins with N-linked glycosylation contain a conversed sequence, asparagine-X-threonine/serine (N-X-T/S). During glycosylation, OST recognizes a nascent polypeptide and attaches the lipid-linked oligosaccharide (LLO) to its asparagine residue.
Figure. Oligosaccharide transfer reactions in eukaryotic cell.
Gilmore G. Structure biology: porthole to catalysis. Nature. 2011 Jun 15; 474 (7351): 292-3.
N-linked glycosylation exits in eukaryotes, archaea and bacteria and it is the most frequent protein modification of membrane and secretory proteins in eukaryotes. Oligosaccharyltransferase (OST) is the central enzyme of N-linked protein glycosylation. OST, it is a heterooligomeric membrane protein complex and exits in animals, plants, fungi, catalyses the glycosylation reaction. In bacteria, archaea and protozoa, OST catalyzes the transfer of a highly defined, LLO (lipid-linked oligosaccharide) donor substrate to a multitude of peptide acceptor sequences located in different substrate proteins. As shown in the figure, in eukaryotes, OST transfers the dolichylpyrophosphate-linked oligosaccharide to the asparagines of an asparagine-X-serine or threonine (N-X-S/T) sequon in the acceptor polypeptide. Truncated, lipid-linked oligosaccharides such as GlcNAc 2 or GlcNAc 2Man also serve as OST substrates. Moreover, OST associates with numerous newly synthesized polypeptide chains now. The human OST complex is composed of seven different polypeptide chains and the heptameric human OST complex contains the subunits ribophorin I (OST1p), ribophorin II (Swp1p), OST48 (Wbp1p), OST4 (OST4), Stt3-A/Stt3-B (Stt3p), N33/Tusc3 and IAP (OST3p and OST6p), and DAD1(OST2p). Among which, Stt3 is the largest and most conserved polypeptide of the OST complex and it is the catalytic subunits of eukaryotic OST complexes. Ribophorin I and II and OST48 are the first identified subunits of the mammalian OST complex. Ribophorin I affects utilization of certain glycosylation sites on defined polypeptides. Ribophorin II is highly conserved in mammals. OST48 can interact with DAD1 and N33/Tusc3 and IAP are two paralogous. OST4 is consisted of a single transmembrane helix. It has been shown that the mutation of OST subunits is related with several diseases. Well understanding and protein engineering of the OST complex provide an access to research some disease mechanisms.
Creative Biostructure can provide custom MemPro™ gene-to-structure services for membrane proteins. Please click for more information.
Elisabeth Mohorko, et al. Oligosaccharyltransferase: the central enzyme of N-linked protein glycosylation. J Inherit Metab Dis. 2011 Aug;34(4):869-78.