Unraveling role of the glucan-binding domain in mutansucrase-mediated glucan synthesis and biofilm-related properties

Mutansucrase (MUS) catalyzes the formation of α-1,3-linked glucan (mutan) from sucrose. Most mutansucrase are produced by Mutan Streptococcus species, which are considered primary etiological agents of dental caries. Previous investigations have posited MUS as one of the crucial virulence factors contributing to biofilm formation. This study investigated the role of the glucan-binding domains (GBDs) in MUS activity and the properties of the resulting glucan product. Our findings showed GBDs rarely participate in α-1,3 glucan elongation and have negligible binding affinity for them. Conversely, GBDs exhibited high affinity for α-1,6 glucans (dextran). Notably, using dextran as an acceptor for α-1,3 glucan extension significantly enhanced MUS transglycosylation and processivity, leading to higher molecular weight glucans and gel-like material formation, emphasizing MUS's role in biofilm development. Although GBDs didn't directly determine glycosidic linkage type, their cooperative interaction with the catalytic domain modulated the physicochemical properties and structural diversity of the synthesized glucans. Furthermore, intrinsic glucan conformation influenced chain elongation, offering a new perspective on biofilm synthesis beyond the enzyme's role. This work also characterized glucans synthesized by MUS via both common sucrose reactions and dextran priming process, providing insights for addressing biofilm challenges and developing new biomaterial applications.