Structural basis of cellulosome efficiency explored by small angle X-ray scattering.
Cellulose, the main structural component of plant cell walls, is the most abundant carbohydrate polymer in nature. To break down plant cell walls, anaerobic microorganisms have evolved a large extracellular enzyme complex termed cellulosome. This megadalton catalytic machinery organizes an enzymatic assembly, tenaciously bound to a scaffolding protein via specialized intermodular "cohesin-dockerin" interactions that serve to enhance synergistic activity among the different catalytic subunits. Here, we report the solution structure properties of cellulosome-like assemblies analyzed by small angle x-ray scattering and molecular dynamics. The atomic models, generated by our strategy for the free chimeric scaffoldin and for binary and ternary complexes, reveal the existence of various conformations due to intrinsic structural flexibility with no, or only coincidental, inter-cohesin interactions. These results provide primary evidence concerning the mechanisms by which these protein assemblies attain their remarkable synergy. The data suggest that the motional freedom of the scaffoldin allows precise positioning of the complexed enzymes according to the topography of the substrate, whereas short-scale motions permitted by residual flexibility of the enzyme linkers allow "fine-tuning" of individual catalytic domains.
Hammel
Michal
M
Architecture et Fonction des Macromolécules Biologiques, Unité Mixte de Recherche 6098, CNRS and Universities Aix-Marseille I and II, 163 Avenue de Luminy, Case 932, F-13288 Marseille Cedex 9, France.
Fierobe
Henri-Pierre
HP
Czjzek
Mirjam
M
Kurkal
Vandana
V
Smith
Jeremy C
JC
Bayer
Edward A
EA
Finet
Stéphanie
S
Receveur-Bréchot
Véronique
V
D001703:Biophysics / Q000379:methods*; D002241:Carbohydrates / Q000737:chemistry; D002384:Catalysis; D020134:Catalytic Domain; D002473:Cell Wall / Q000378:metabolism; D002482:Cellulose / Q000737:chemistry; D044603:Cellulosomes / Q000737:chemistry*; D046973:Ruminiclostridium cellulolyticum / Q000201:enzymology; D003094:Collagen / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D011108:Polymers / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D013379:Substrate Specificity; D014965:X-Rays
D002241:Carbohydrates; D011108:Polymers; D011993:Recombinant Fusion Proteins; D002482:Cellulose; D003094:Collagen