The cohesin-dockerin interaction was originally discovered as the decisive modular pair that dictates the assembly of the various enzymatic subunits into the cellulosome complex. Until recently, the presence of cohesins and dockerins within a bacterial proteome was considered a definitive “signature” of a cellulosome-producing bacterium. The surprising discovery of cellulosome-like sequences in Archaeoglobus fulgidus changed all that! Widespread genome sequencing has since revealed a wealth of putative cohesin- and dockerin-containing proteins in bacteria, archaea and in primitive eukaryotes (Table). The newly identified modules appear to serve diverse functions that are clearly distinct from the classical cellulosome archetype, and the vast majority of parent proteins are not predicted glycoside hydrolases. In most cases, only a few such genes have been identified in a given microorganism, which encode proteins containing but a single cohesin and/or dockerin. In some cases, the proteins of a given species contain only cohesins and dockerins appear to be missing. In others, only dockerins are present in the proteins of a given species. Sometimes, both modules occur within the same protein. The attached table provides a bioinformatics-based survey of the current status of cohesin- and dockerin-like sequences in species from the Bacteria, Archaea, and Eukarya. Surprisingly, many identified modules and their parent proteins are clearly unrelated to cellulosomes. For example, the cohesins and dockerins of the human pathogen, Clostridium perfringens, are associated with a series of enzymatic toxins. None of the newly discovered proteins exhibit multiple cohesins which would then form a scaffoldin subunit. The cellulosome paradigm may thus be the exception rather than the rule for bacterial, archaeal, and eukaryotic employment of cohesin and dockerin modules. We continue to study such non-cellulosomal cohesin and dockerin components to determine the extent of their occurrence, diversity and function in nature
Table: Non-cellulosomal Cohesin - and Dockerin-like Modules(PDF)
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- Chitayat, S., Gregg, K., Adams, J. J., Ficko-Blean, E., Bayer, E. A., Boraston, A. B., and Smith, S. P. (2008) Three-dimensional structure of a putative non-cellulosomal cohesin module from a Clostridium perfringens family 84 glycoside hydrolase. J. Mol. Biol. 375, 20-28.
- Chitayat, S., Adams, J. J., Furness, H. S., Bayer, E. A., and Smith, S. P. (2008) The solution structure of the C-terminal modular pair from Clostridium perfringens reveals a non-cellulosomal dockerin module. J. Mol. Biol. 381, 1202-1212.
- Adams, J. J., Gregg, K., Bayer, E. A., Borasston, A. B., and Smith, S. P. (2008) Structural basis for a novel mode of Clostridium perfringens toxin complex formation. Proc. Natl. Acad. Sci. USA 105, 12194-12199.
Peer, A., Smith, S. P., Bayer, E. A., Lamed, R., and Borovok, I. (in press) Non-cellulosomal cohesin and dockerin-like modules in the three domains of life. FEMS Microbiol. Lett.