A minimal cellulosome-like system in Cellulosilyticum lentocellum

Cellulosomes are efficient enzymatic nanomachines which have arisen for the degradation of cellulosic biomass. They are found abundantly in soil-dwelling microbes and bacteria which thrive in the stomachs of ruminant mammals. Two protein domains, cohesins and dockerins, characterise cellulosomes. These domains interact with each other to form, in many cases, enormous complexes with as many as 160 individual proteins. However, genome annotation of Cellulosilyticum lentocellum DSM 5427 revealed a single cohesin domain (encoded by Clole_2599) and a single dockerin domain (Clole_2598). Therefore, we recombinantly expressed ClcC and ClcD and found they form a (predicted ~ 104 kDa) heterodimeric complex. We show that this complex formation enhances cellulase activity approximately 2-fold on insoluble microcrystalline cellulose and 1.25-fold on soluble carboxymethyl cellulose. Moreover, we identified two additional candidate interacting partners for ClcC, one of which appears to bind via a non-canonical interface. These findings suggest that cellulosomal principles can operate in highly reduced cohesin-dockerin systems.