Enzymatic Control of Polymerization Shapes the Structural Assembly of Bottom-Up Synthesized Cellulose

High Resolution Image Download MS PowerPoint Slide Cellodextrin phosphorylases (CdPs) are powerful catalysts for the precision synthesis of short-chain cellulose, yet the structural origins of their distinct polymerization behavior remain unclear. Herein, we show that variations in the molecular architecture of the CdP substrate-binding pocket control cellulose chain polymerization and, in turn, affect chain assembly in solution. Across a phylogenetically diverse set of CdPs, we observe pronounced enzyme-dependent divergence in chain extension: some enzymes terminate at short, narrowly distributed cello-oligomers (DP 6-15), whereas others support progressive growth beyond DP 20 with broad length distributions. Structural modeling and mutagenesis identify binding-pocket configuration as a primary determinant of this behavior. Localized steric and hydrophobic barriers associated with conserved aromatic residues destabilize extended intermediates along the chain-extension path in restrictive CdPs, whereas more permissive pockets support a continuous binding mode that enables sustained extension. CdP concentration further modulates this process by controlling productive chain rebinding to the enzyme vs premature aggregation in solution. Importantly, these molecular effects propagate to the level of higher-order cellulose assembly: narrow DP distributions primarily yield cellulose II-type nanosheet structures, whereas broader distributions are associated with notable structural and morphological variations, including changes in diffraction profiles, nanoscale dimensions, and aggregation behavior. Together, these results identify CdP binding-pocket architecture as a key determinant of cellulose chain length and higher-order structural/morphological organization, providing a basis for the bottom-up enzymatic design of cellulose materials.