Structural insights into the mechanism of pH-selective substrate specificity of the polysaccharide lyase Smlt1473

• DOI: 10.1016/j.jbc.2021.101014
• Publication Date: 2021-08-03T15:30:23Z
• Authors: Shubhant Pandey; Pranjal Mahanta; Bryan W. Berger; Rudresh Acharya
• Keywords: 0301 basic medicine; Structure-Activity Relationship; 03 medical and health sciences; Bacterial Proteins; Protein Domains; Stenotrophomonas maltophilia; Hydrogen-Ion Concentration; Research Article; Polysaccharide-Lyases; Substrate Specificity

Polysaccharide lyases (PLs) are a broad class of microbial enzymes that degrade anionic polysaccharides. Equally diversity in their polysaccharide substrates has attracted interest biotechnological applications such as biomass conversion to value-added chemicals and biofilm removal. Unlike other PLs, Smlt1473 present the clinically relevant Stenotrophomonas maltophilia strain K279a demonstrates wide range pH-dependent substrate specificities toward multiple, diverse polysaccharides: hyaluronic acid (pH 5.0), poly-β-D-glucuronic (celluronic) 7.0), poly-β-D-mannuronic acid, poly-α-L-guluronate 9.0). To decode pH-driven multiple selectivity this single enzyme, we X-ray structures determined at pH values apo mannuronate-bound states well tetra-hyaluronate-docked structure. Our results indicate structural flexibility binding site N-terminal loop coupled with specific stereochemistry facilitates distinct modes entry for having charge densities chemical structures. analyses wild-type solved different (5.0-9.0) pH-trapped (5.0 7.0) catalytically mannuronate complexes (1) modulates catalytic microenvironment guiding structurally chemically substrates, (2) further establish molecular-level fluctuation enzyme tunnel is preconfigured, (3) suggest fluctuations resulting optimal cleavage. Furthermore, our provide key insight into how strategies reengineer both flexible regions distal active could be developed target new applications.