Oligosaccharide moiety from the disialylated glycosphingolipid GD1a of a-series, which is one of the major gangliosides in neuronal and glial membranes. It interacts with myelin-associated glycoprotein (MAG) and is essential for long-term axon-myelin stability. It plays a role in viral infection since it is a receptor for viral glycoproteins in rotavirus and paramyxovirus 1. The hexasaccharide GD1a moiety was also found on a glycoprotein that acts as a receptor for adenovirus type 37. GD1a ganglioside also interacts with botulinum neurotoxin (BoNT) and is crucial for its entry into cells.