Sialylation reactions take place in the lumen of the Golgi apparatus where
sialyltransferases (STs) decorate glycan moieties of both the cell surfaces associated and
secreted proteins and lipids with sialic acids (Sia) predominantly, but not exclusively
employing, CMP-Neu5Ac as donor substrate. Because of its physical and chemical
properties, CMP-Neu5Ac is unable to diffuse across the Golgi membrane and must be
translocated from the cell cytosol into the lumen of the Golgi apparatus. Such
translocation is performed by the CMP-Sia transporter, a member of an evolutionary
conserved family of proteins together referred to as nucleotide sugar transporters.
Although several nucleotide sugar transporters, including the CMP-Sia transporter, have
been biochemically characterized over the last 30 years, the lack of a three-dimensional
structure of any nucleotide sugar transporter requires alternative approaches to
elucidating the structure-function relationship of this class of protein. We describe in
this chapter the latest data reporting the elucidation of CMP-Sia transporter structurefunction
relationship.
Keywords: CMP-sialic acid transporter, Nucleotide sugar transporters, Golgi
apparatus, CMP-sialic acid transporter structure-function, Saturation Transfer
Difference NMR, CMP-N-acetylneuraminic acid, trans-membrane domains.
