Ultrastructural diversity of the cellulase complexes of Clostridium papyrosolvens C7

Abstract

Transmission electron microscopy was used to investigate the ultrastructural features of diverse cellulase and cellulase-xylanase multiprotein complexes that are components of the cellulase-xylanase system of Clostridium papyrosolvens C7. The multiprotein complexes were separated by anion-exchange chromatography into seven biochemically distinguishable fractions (F1 to F7). Most individual F fractions contained, in relatively large numbers, an ultrastructurally recognizable type of particle that occurred only in smaller numbers, or not at all, in the other F fractions. It is suggested that these ultrastructurally distinct particles represent the biochemically distinct multiprotein complexes that constitute the cellulase-xylanase system of C. papyrosolvens C7. Some of the particles consisted of tightly packed globular components that appeared to be arranged in the shape of a ring with conical structures pointing out along its axis. Other particles had triangular, polyhedral, or star shapes. The major protein fraction (F4) almost exclusively contained particles consisting of loosely aggregated components, many of which appeared to be arranged along filamentous structures. The ultrastructural observations reported here support our previous conclusion that the cellulase-xylanase system of C. papyrosolvens C7 comprises at least seven different high-molecular-weight multiprotein complexes. Furthermore, results of this and earlier studies indicate that the interactions between C. papyrosolvens C7 and cellulose are different from those that have been described for Clostridium thermocellum.The extracellular cellulase-xylanase system of Clostridium papyrosolvens C7 comprises at least seven distinct high-molecular-weight multiprotein complexes (M r , 500,000 to 660,000), each with different polypeptide compositions and enzymatic properties (16). All seven multiprotein complexes have endoglucanase-active protein subunits, but only two of the complexes have xylanase-active subunits (16). Three of the multiprotein complexes hydrolyze crystalline cellulose (i.e., have Avicelase activity) (16). Arabinofuranosidase, ␤-xylosidase, and acetylesterase activities were detected in cellulase-and xylanase-active complexes (17). Hydrolysis of crystalline cellulose by C. papyrosolvens C7 involves synergistic interactions in which the diverse multiprotein complexes participate (16).Cellulolytic bacteria, such as C. papyrosolvens C7, inhabit natural environments in which cellulose is present primarily in plant cell walls in association with other polysaccharides or polymers (e.g., xylan and other hemicellulose components) (13, 16). Generally, anaerobic bacteria that degrade plant cell wall material synthesize extracellular multiprotein complexes that function in the concurrent hydrolysis of different plant polysaccharides. The cellulase-xylanase system of C. papyrosolvens C7 differs from previously described cellulose-hydrolyzing systems of other anaerobic bacteria in that it includes diverse multiprotein complexes, i.e., it is a multicomp...

Determination of Subunit Composition of Clostridium cellulovorans Cellulosomes That Degrade Plant Cell Walls

“…Moreover, the enzymatic activities in the fractions were also different. These results indicated that C. cellulovorans grown with pectin produced heterogeneous cellulosomes, as has been shown with C. papyrosolvens C7 cellulosomes (17,18).…”

“…So far, it has been observed that carbon sources in the medium have an effect on enzymatic activity and enzyme composition (15,23). Pohlschroder et al reported that Clostridium papyrosolvens C7 produces at least seven different forms of cellulosomes and that each type of cellulosome has a different enzymatic activity (17,18). These results indicate that Clostridium species actually produce heterogeneous cellulosomes and that the enzymatic activity of each cellulosome depends on its subunit composition.…”

Cellulosomes from Mesophilic Bacteria

“…The different subunits in these populations represented the presence of a large number of different cellulosomal enzymes. Furthermore, when these populations were examined by transmission electron microscopy, each population had a distinct morphology, again indicating a difference in subunit composition of these complexes (51). It seems clear at this time that cellulosomes are heterogeneous in enzymatic subunit composition and that in nature this may help the bacteria to degrade a complex substrate such as plant cell walls very efficiently.…”

Cellulase, Clostridia, and Ethanol

“…In C. papyrosolvens, a mesophilic anaerobe, the cellulase system (53) can be fractionated by ion-exchange chromatography into seven high-molecular-weight multiprotein complexes, with the molecular weights ranging from 500,000 to 600,000. Each complex has a different ultrastructure (269) and a unique profile of enzymatic activities (270). The common protein appearing in each fraction is a glycoprotein (M r ϭ 125,000) that lacks any enzymatic activity.…”