Scaffoldins

Scaffoldins are non-catalytic structural proteins that organize cellulolytic enzymes into cellulosomes, large extracellular multi-enzyme complexes produced by certain cellulolytic bacteria and some archaea. In these systems, scaffoldins contain multiple cohesin domains that bind dockerin-containing catalytic enzymes, enabling the assembly of diverse enzyme cocktails on a single scaffold. The cohesin–dockerin interactions are highly specific, allowing enzymes to be arranged in defined patterns to optimize enzymatic synergy.

Primary scaffoldins anchor to the cell surface or cell wall through binding motifs and recruit catalytic units via dockerin–cohesin interactions. Adaptor scaffoldins lack catalytic domains but provide additional docking sites to expand enzyme repertoires or to connect the complex to the cell surface. Some scaffoldins also carry carbohydrate-binding modules to tether the entire complex to polysaccharide substrates, increasing local enzyme concentration and substrate contact.

Functionally, scaffoldins enable proximity and coordinated action among a suite of enzymes that degrade plant polysaccharides, enhancing the efficiency of cellulose hydrolysis. This architectural organization is fundamental to the cellulosome concept and underpins the high catalytic output observed in certain anaerobic bacteria.

In research and biotechnology, scaffoldins have informed strategies to engineer artificial cellulosomes and optimize enzyme mixtures for biomass conversion and biofuel production. Classic model organisms include species such as Clostridium cellulolyticum and Ruminococcus flavefaciens, with genome analyses revealing extensive repertoires of scaffoldin and dockerin-containing enzymes.

See also: cellulosome, dockerin, cohesin, cellulase.