Glycosyltransferase family 52. This family features glycosyltransferases belonging to glycosyltransferase family 52, which have alpha-2,3- sialyltransferase (EC:4.2.99.4) and alpha-glucosyltransferase (EC 2.4.1.-) activity. For example, beta-galactoside alpha-2,3- sialyltransferase expressed by Neisseria meningitidis is a member of this family and is involved in a step of lipooligosaccharide biosynthesis requiring sialic acid transfer; these lipooligosaccharides are thought to be important in the process of pathogenesis. This family includes several bacterial lipooligosaccharide sialyltransferases similar to the Haemophilus ducreyi LST protein. Haemophilus ducreyi is the cause of the sexually transmitted disease chancroid and produces a lipooligosaccharide (LOS) containing a terminal sialyl N-acetyllactosamine trisaccharide.
Alpha-2,8-polysialyltransferase (POLYST). This family contains the bacterial enzyme alpha-2,8-polysialyltransferase (EC:2.4.99.-) (approximately 500 residues long). This catalyzes the polycondensation of alpha-2,8-linked sialic acid required for the synthesis of polysialic acid (PSA).
Two tandem repeats of the cystathionine beta-synthase (CBS pair) domains found associated with the ABC transporter OpuCA. This cd contains two tandem repeats of the cystathionine beta-synthase (CBS pair) domains found in association with the ABC transporter OpuCA. OpuCA is the ATP binding component of a bacterial solute transporter that serves a protective role to cells growing in a hyperosmolar environment but the function of the CBS domains in OpuCA remains unknown. In the related ABC transporter, OpuA, the tandem CBS domains have been shown to function as sensors for ionic strength, whereby they control the transport activity through an electronic switching mechanism. ABC transporters are a large family of proteins involved in the transport of a wide variety of different compounds, like sugars, ions, peptides, and more complex organic molecules. They are a subset of nucleotide hydrolases that contain a signature motif, Q-loop, and H-loop/switch region, in addition to the Walker A motif/P-loop and Walker B motif commonly found in a number of ATP- and GTP-binding and hydrolyzing proteins. The CBS domain, named after human CBS, is a small domain originally identified in cystathionine beta-synthase and is subsequently found in a wide range of different proteins. CBS domains usually occur in tandem repeats. They associate to form a so-called Bateman domain or a CBS pair based on crystallographic studies in bacteria. The CBS pair was used as a basis for this cd hierarchy since the human CBS proteins can adopt the typical core structure and form an intramolecular CBS pair. The interface between the two CBS domains forms a cleft that is a potential ligand binding site. The CBS pair coexists with a variety of other functional domains and this has been used to help in its classification here. It has been proposed that the CBS domain may play a regulatory role, although its exact function is unknown. Mutations of conserved residues within this domain are associated with a variety of human hereditary diseases, including congenital myotonia, idiopathic generalized epilepsy, hypercalciuric nephrolithiasis, and classic Bartter syndrome (CLC chloride channel family members), Wolff-Parkinson-White syndrome (gamma 2 subunit of AMP-activated protein kinase), retinitis pigmentosa (IMP dehydrogenase-1), and homocystinuria (cystathionine beta-synthase).
