CBM47

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Enzymes that degrade host glycans are increasingly being found as virulence factors in pathogenic bacteria[1][2]. A common property of extracellular glycan degrading enzymes found in such bacteria is multi-modularity; these enzymes often comprise a large number of modules with a variety of functions. The most common class of ancillary module are carbohydrate-binding modules (CBMs)[3], which are alternatively referred to as lectin-domains. These modules are responsible for targeting carbohydrate-degrading enzymes to a glycan substrate or, when the enzymes are attached to the bacterial cell-surface, likely also function to adhere the bacterium to a glycan[4]. The presence of these lectin-domains in multi-modular proteins and their contribution of glycan binding function to catalytically active proteins distinguishes these modules from other bacterial glycan-binding proteins (GBPs). The CBM47 modules from the Streptococcus pneumoniae enzyme SpGH98 (or "fucolectin-related protein") are specific to the Lewisy antigen[5], which is quite rare among all GBPs, and function to target this enzyme to this antigen when present on epithelial cells[6]. Recognition and destruction of this antigen appears to be a critical process in pneumococcal virulence[2][7].

Contents

CFG Participating Investigators contributing to the understanding of this paradigm

This is a very new area of investigation. CFG Participating Investigators (PIs) that have screened other CBMs or proteins containing CBMs include: Alisdair Boraston, Garry Taylor, Warren Wakarchuck

Progress toward understanding this GBP paradigm

This section documents what is currently known about CBM47, its carbohydrate ligand(s), and how they interact to mediate cell communication.

Carbohydrate ligands

CBM47 is a fucose specific binding module that is related to Anguilla anguilla fucolectin. The high affinity ligand for CBM47 has been determined from glycan microarray screening on the CFG microarray[1]to be Fucα1-2Galβ1-4(Fucα1-3)GlcNAc [Lewis y][5].

File:Lewisy.jpg

Cellular expression of GBP and ligands


Biosynthesis of ligands


Structure

CBM47 originates from a multimodular S. pneumoniae that has an N-terminal, Lewisy degrading catalytic module. Indeed, three CBM47 modules are found in tandem.

File:modular.jpg

The high resolution X-ray structures of the N-terminal and C-terminal CBM47 modules have been determined and the N-terminal module in complex with the Lewisy tetrasaccharide[5].

File:CBM47.jpg


Biological roles of GBP-ligand interaction

The primary role of CBM47, and indeed other CBMs found in carbohydrate-active enzymes, is to direct the entire enzyme to its glycan substrate. However, CBMs found in carbohydrate-active enzymes attached to microbial cell surfaces may also play a role in the adhesion of the bacterium to host glycan-bearing tissues.

CFG resources used in investigations

The best examples of CFG contributions to this paradigm are described below, with links to specific data sets. For a complete list of CFG data and resources relating to this paradigm, see the CFG database search results for CBM.

Glycan profiling


Glycogene microarray


Knockout mouse lines

Not applicable.

Glycan array

The specificity of several CBMs have been investigated by CFG glycan array analysis (click here for example). Isolated glycans for structural and quantitative binding studies have also been obtained from the CFG.

Related GBPs

There are presently over 55 families of CBMs that are defined on the basis of amino acid sequence similarity; however, the majority of these CBMs families contain members specific for plant cell wall polysaccharides. CFG resources have been instrumental in studying the subset of CBMs that recognize complex glycans. In addition to CBM47 there are a number of CBMs belonging to family 32 and 51 that share the property of binding complex glycans. Though unrelated at the amino acid sequence level CBMs in families 32, 47, and 51 are structurally related and functionally related. It is important to note, however, that the diversity of complex glycan binding among these family members is considerable and only coming to light through glycan array screening. The availability of purfied glycans is facilitating structural and quantitative studies of glycan binding by CBMs in families 32, 47, and 51.

References

  1. Shelburne, S. A., Davenport, M. T., Keith, D. B. & Musser, J. M. (2008). The role of complex carbohydrate catabolism in the pathogenesis of invasive streptococci. Trends Microbiol 16, 318-25.
  2. 2.0 2.1 Hava, D. L. & Camilli, A. (2002). Large-scale identification of serotype 4 Streptococcus pneumoniae virulence factors. Mol Microbiol 45, 1389-406.
  3. Boraston, A. B., Bolam, D. N., Gilbert, H. J. & Davies, G. J. (2004). Carbohydrate-binding modules: fine tuning polysaccharide recognition. Biochem J 382, 769-782.
  4. Ficko-Blean, E., Gregg, K. J., Adams, J. J., Hehemann, J. H., Czjzek, M., Smith, S. P. & Boraston, A. B. (2009). Portrait of an enzyme, a complete structural analysis of a multimodular {beta}-N-acetylglucosaminidase from Clostridium perfringens. J Biol Chem 284, 9876-84.
  5. 5.0 5.1 5.2 Boraston, A. B., Wang, D. & Burke, R. D. (2006). Blood group antigen recognition by a Streptococcus pneumoniae virulence factor. J Biol Chem 281, 35263-35271.
  6. Higgins, M. A., Whitworth, G. E., El Warry, N., Randriantsoa, M., Samain, E., Burke, R. D., Vocadlo, D. J. & Boraston, A. B. (2009). Differential recognition and hydrolysis of host carbohydrate antigens by Streptococcus pneumoniae family 98 glycoside hydrolases. J Biol Chem 284, 26161-73.
  7. Embry, A., Hinojosa, E. & Orihuela, C. J. (2007). Regions of Diversity 8, 9 and 13 contribute to Streptococcus pneumoniae virulence. BMC Microbiol 7, 80.

Acknowledgements

The CFG is grateful to the following PIs for their contributions to this wiki page: Alisdair Boraston, Anne Imberty

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