Cellulose Synthesis

• biofilm matrix are called EPS and consist of polysaccharides, proteins and DNA -> these form a structural scaffold to hold the biofilm together
• all gram negative bacteria or type of exopolysaccharide system, they all need c-di-GMP to activate their exopolysaccharide synthase machineries

  
• cellulose is a linear polymer of beta 1,4 linked glucose and possess many H bond donors which results in high capacity for water binding, UDP glucose is the substrate for cellulose synthesis where the glucose is removed and linked into a polymer
• the biosynthesis and export of cellulose is achieved by a synthase dependent mechanism consisting of 4 components

  • BcsA -> 2 domains to synthesize cellulose
  • glycosyl transferase which turns UDP glucose into glucose to incorporate into cellulose chain
  • enzyme domain that binds c-di-GMP to adopt catalytically active conformation
  • BcsB ->membrane transporter and periplasmic scaffold to transfer through peptidoglycan layer
  • BcsZ -> cellulase which digests improper/excess cellulose in peptidoglycan layer
  • BcsC -> outer membrane porin to push cellulose out of membrane

  
• BcsA (activated by c-di-GMP) and BcsB complexes to catalyze the polymerization and translocation of cellulose across the inner membrane

  
• BcsA active site has a residue R580 which interacts with the gating loop to keep it blocking the UDP glucose active site but when c-di-GMP binds to c-di-GMP binding site it interacts with R580 forming 2 H bonds which outcompetes R580 with gating loop which opens to let UDP glucose enter the active site

  • BcsA bound to c-di-GMP -> gating loop unblocks UDP glucose active site