Glycoproteins in prokaryotes
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© Springer-Verlag 1997
MINI-REVIEW
Sara Moens · Jos Vanderleyden
Glycoproteins in prokaryotes
Received: 24 February 1997 / Accepted: 13 May 1997
Abstract Rather recently it has become clear that prokaryotes (Archaea and Bacteria) are able to glycosylate proteins. A literature survey revealed the different types of glycoproteins. They include mainly surface layer (S-layer) proteins, flagellins, and polysaccharide-degrading enzymes. Only in a few cases is structural information available. Many different structures have been observed that display much more variation than that observed in eukaryotes. A few studies have given evidence for the function of the prokaryotic glycoprotein glycans. Also from the biosynthetic point of view, information is rather scarce. Due to their different cell structure, prokaryotes have to use mechanisms different from those found in eukaryotes to glycosylate proteins. However, from the fragmented data available for the prokaryotic glycoproteins, similarities with the eukaryotic system can be noticed.
view Lechner and Wieland (1989)]. More recently, evidence has also been provided for the occurrence of glycoproteins in Bacteria. The best-studied examples of bacterial glycoproteins are surface-layer (S-layer) proteins (Messner and Sleytr 1991). Non-S-layer glycoproteins (Sandercock et al. 1994) have been reported, but only in a few cases have structural studies been performed. These studies have concerned mainly enzymes involved in the degradation of polysaccharides. Table 1 gives an overview of the reported prokaryotic glycoproteins. Experimental evidence for the glycoprotein nature is not always very convincing and has, in some cases, already been proved to be incorrect [e.g., Kimura and Stadtman (1995)]. Due to the abundance of glycans in most prokaryotic cell walls, extensive purification is needed in most cases. The final proof for the glycosylation of a protein is the identification of the linkage unit (amino-acid-attached sugar).
Key words Glycoprotein · Glycosylation · Bacteria · Archaea
Structural aspects of prokarytic glycoproteins Abbreviation S-layer Surface layer
Occurrence of glycoproteins in prokaryotes While glycosylation of proteins in eukaryotes has been studied for a long time, glycosylation of proteins in prokaryotes is a rather recent research topic. Prokaryotes were considered for a long time to be unable to glycosylate proteins. It is now, however, clear that glycoproteins are widespread in both the domain of the Archaea and the domain of the Bacteria. The first chemically characterized example of a prokaryotic glycoprotein was the cell surface protein of the archaeon Halobacterium halobium [re-
S. Moens · J. Vanderleyden (Y) F. A. Janssens Laboratory of Genetics, Catholic University of Leuven, Willem de Croylaan 42, B-3001 Heverlee, Belgium Tel. +32-1632-2403; Fax +32-1632-2990 e-mail: [email protected]
We have only limited information about the possible structures of the prokaryotic glycoproteins, but from the available data it is obvious that the
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