Over 3000 E-Learning topics / 5000 Articles & Applications
 

Glycoform Variation in N-Linked Glycans

Deamidation
Figure 1: Glycoform variation in N-linked glycans

N-glycosylation involves the addition of a glycan (oligosaccharide sugar moiety) to the nitrogen in the amide of asparagine. Recent studies of antibody glycosylation in vitro have confirmed that this particular PTM is essential to generate the specific glycoform (isoforms of the glycosylated antibody) that the mAb effector functions require to initiate the appropriate immune response to an antigen. Aglycosylated mAbs (with no oligosaccharides) are largely non-functional, with minimal effector functions likely due to conformational changes induced by the lack of the necessary glycan. They also tend to be highly unstable, with an increased likelihood of aggregation.

In mAbs, it is a specific glycosylation at asparagine residue 297 (Asn-297) within the Fc region of the antibody heavy chains that must occur. The different characteristics of the glycan attached to the mAb at this point has a considerable impact on the overall conformation of the antibody, and hence plays a vital role in the specificity and selectivity of antigen binding. There is extensive heterogeneity across the oligosaccharides involved in mAb glycosylation, resulting in potentially 400+ different mAb glycoforms from Fc glycosylation alone.

Glycosylation of asparagine in the variable section of Fab antibody region is also possible, and may have either positive or negative effects on antigen binding depending on the specific modifications; the oligosaccharide itself and the position of the asparagine both influence overall antigen affinity.


mAb Fc glycoforms
Figure 2: Example of a small number of the different types of oligosaccharides that may be attached to a mAb. The huge variety of combinations results in over 400 different mAb Fc glycoforms

 
NANA - N-acetylneuraminic (sialic) acid NGNA - N-glycolylneuraminic acid
 
Man - mannose GlcNAc - N-acetylglucosamine
Xyl-1,2 - 1,2-Xylitol
Gal - galactose Xyl-1,2 - 1,2-xylitol 1,6-fucose
Figure 2: post translational modifications

A common component of N-glycosylation at the Fc Asn-297 position is a fucose (hexose deoxy sugar) core; fucosylation is one of the most common oligosaccharide modifications of antibodies. However, mAbs with no fucose core (afucosylated) have increased efficacy in terms of antibody-dependent cellular cytotoxicity (ADCC), when compared to the equivalent fucosylated mAb.

Therefore, specific mammalian cell lines able to produce afucosylated mAbs have been developed to enable controlled fucosylation in future development of mAb biopharmaceuticals that require an ADCC response for optimal success.

Other post-translational modifications include o-linked glycosylation, usually involving smaller oligosaccharide units attached to serine or threonine residues and typically in the variable region. N-linked glycan PTMs are also found in the V and CH1 domains with the former variant usually involving sialic acids (NANA, NGNA).

 
loading data
loading data
loading data
loading data
loading data
 
 
 
 
 Home | About UsContact Us | SubscribeTerms and Conditions | Advertise | Privacy Policy 
iiiiiii

loading data

loading data

 

loading data


loading data