Six N-acetylglucosaminyltransferases (GlcNAc-T) are responsible for the addition of GlcNAc to the growing complex type sidechains. (Brockhausen, Schachter 1988) All of them, but GlcNAc-T V, are Mn2+ dependent.
The following is a list of the six GlcNAc-T and the terminal sugars on the branches after their action:
In short:
Recent investigations have led to a plausible model to explain the metastatic potential of transformed cells. Associated with several types of cancers an increased amount of poly-N-acetyllactosamine sidechains on tetraantennary structures has been found. In correlation with this increased expression of GlcNAc-T V was detected which led to the formation of tetraantennary structures on which beta-1,3 N-acetylglucosaminyltransferase can then act. Following this SiaLeX epitopes can be formed at the non-reducing termini, these epitopes play a major role in the adhesion of cells (e.g. leucocytes) to selectins. (Fukuda 1992 and references therein)
In the course of these studies it has also been shown that a certain correlation between the expression of the ras proto oncogen and the level of expression of GlcNAc-T V exists. (Easton 1991, Yousefi 1991)
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Written by: Christian Frosch
frosch@mzdmza.zdv.uni-mainz.de
http://www.uni-mainz.de/~frosc000
Institute of Toxicology
University of Mainz
Last update: 09.07.1995