Sialyltransferase CstII/CMP-NeuAc complex
Campylobacter jejuni (bacteria)
Glycoconjugates, such as glycoproteins, glycolipids and polysaccharides, are present on the cell surfaces of many organisms and participate in cell-cell recognition, cell differentiation and various receptor-ligand interactions. They contain essential nine-carbon sugars known as sialic acids. Sialic acids such as N-acetyl-neuraminic acid (NueAc) terminate oligosaccharide chains, playing important roles in cell recognition and adherence to cell surfaces. Glycolipids including sialic acids, gangliosides, have been found in all vertebrate cell types. They are therefore considered as the essential glycans of the nerve cells. They act as receptors for microorganisms and bacterial toxins, regulate cell growth and differentiation, and contribute to cell-cell interactions. It has been suggested that gangliosides act as a trigger for autoimmune mechanisms in the development of Guillain-Barre syndrome. The terminal sialic acids of gangliosides play an essential role in the expression of these structural diversities. The membrane-associated enzymes, sialyltransferases, transfer the sialic acids to the terminal positions of glycoconjugates. Therefore, one can assume that these enzymes might be suitable targets for therapeutic intervention.
The structure of CstII, a sialyltransferase from Campylobacter jejuni, which is a human mucosal pathogen and expresses various cell surface carbohydrates of gangliosides associated with virulence, has been determined. This enzyme transfers the terminal NueAc of cytidine-5'-monophospho-N-acetyl-neuraminic acid (CMP-NueAc), which is a donor of the sialic acid, to the terminal position of glycoconjugates acting as an acceptor. This is also the first structure of a sialyltransferase. The structure, the first structure sialyltransferase reported, consists of a homo-tetramer with the substrates, CMP-NueAc. CtsII from this particular strain used in this study is a bi-functional enzyme; it first transfers sialic acid and then also transfers a second sialic acid from another donor to the terminal position of the first sialic acid-glycoconjugate complex. This mechanism differs from the one observed in the enzymes from other strains, because they act as mono-functional enzymes. The structure analysis of this enzyme moreover has provided a framework for the structure-based design of specific inhibitors.
Protein Data Bank (PDB)
Chiu, C.P. Watts, A.G. Lairson, L.L. Gilbert, M. Lim, D. Wakarchuk, W.W. Withers, S.G. Strynadka, N.C.; "Structural analysis of the sialyltransferase CstII from Campylobacter jejuni in complex with a substrate analog."; Nat.Struct.Mol.Biol.; (2004) 11:163-170 PubMed:14730352.
author: Yuko Tsuchiya