5-30: Understanding the cellulosome enzyme complex

Most bacteria and fungi use free enzymes to degrade plant cell walls in nature. However, some bacteria have adopted a different approach where enzymes are free or tethered on a large protein scaffold forming a complex called the cellulosome. The study of these large protein assemblies is an ongoing research topic that has already yielded numerous breakthroughs. However, the mechanism of assembly for the enzyme subunits of the natural scaffoldin, the modes of action of the cellulosome, and its enzymatic components are not currently well understood.

In this study we focused on the cellulosome-integrating protein CipA of C. thermocellum and cellulosomal enzymes from families 5, 9 and 48. These three enzymes are representative of the variety of enzymes secreted by C. thermocellum. This work aims at understanding the mechanisms involved in the sequential binding of the cellulosomal enzymes to the CipA scaffold of C. thermocellum but also the binding of CipA to secondary scaffolds. A large study of the effect of several key physical properties on binding to the scaffoldin protein is conducted.  The modularity of the enzymes was found to be one of the main influences on the cellulosome assembly process. Additionally, several key sub-modules of the large multi-modular family 9 enzyme, CbhA, including the X1, CBM4 and the immunoglobulin-like modules were studied using molecular dynamics and small angle x-ray scattering.

Y. J. Bomble, G. T. Beckham, J. F. Matthews, M. R. Nimlos, M. E. Himmel, and M. F. Crowley (2010) J. Biol. Chem. (DOI: 10.1074/jbc)