Sas20 is a highly flexible starch-binding protein in the Ruminococcus bromii cell-surface amylosome

TheRuminococcus bromiiamylosome protein Sas6 binds single and double helical α-glucan structures in starch

“…The cognate cohesin for the Sas6 dockerin is unknown. Sas6 is detected in the cell-free supernatant of R. bromii cultures in stationary phase but also elutes from the surface of exponentially growing cells with EDTA which disrupts the calcium-dependent cohesin-dockerin interaction [17, 29]. To determine the localization of Sas6, we grew cells to mid-log phase on potato amylopectin and performed a Western Blot with custom antibodies against recombinant Sas6 ( Fig.…”

Sticking to starch

“…The recent work of Koropatkin et al. on the starch-binding proteins of the anaerobic bacterium Ruminococcus bromii comprises an exciting new facet of the structure–function analysis of complex carbohydrate utilization systems from the HGM ( 6 ). R. bromii is an important “keystone” member of the HGM that can crossfeed other species through the primary degradation of resistant starches ( 7 , 8 ), that is, the α-glucan polysaccharides that escape hydrolysis by human amylases ( 9 ).…”

“…Cerqueira et al. ( 6 ) noted that the R. bromii genome encodes five scaffoldins and 27 dockerin-containing proteins, five of which can be confidently predicted as amylases (starch glycosidases) based on membership in Glycoside Hydrolase Family 13. The remaining 22 comprise a group of proteins of unknown function, 00whose role in the amylosome is obscured by poor sequence similarity.…”

“…Through a detailed modular dissection and biophysical analysis of Sas20 and Sca5, including polysaccharide affinity gel electrophoresis and isothermal titration calorimetry, Cerqueira et al. ( 6 ) conclusively demonstrated that Sas20d1, Sas20d2, and Sca5X25-2 are indeed novel starch-binding domains. Furthermore, protein crystallography of Sas20d1 and Sca5X25-2 revealed distinct protein folds.…”

“…In the broader context of HGM metabolism, the recent work of Cerqueira et al. ( 6 ) is particularly revelatory in highlighting the tertiary structural commonality of the starch capture systems across taxa in the absence of strong primary structure similarity. Viz.…”