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Publication Abstract from PubMed

Gum arabic (GA) is widely used as an emulsion stabilizer and coating in several industrial applications, such as foods and pharmaceuticals. GA contains a complex carbohydrate moiety, and the non-reducing ends of the side chains are often capped with l-rhamnose; thus, enzymes that can remove these caps are promising tools for the structural analysis of the carbohydrates comprising GA. In this study, GA-specific l-rhamnose-alpha-1,4-d-glucuronate lyase from the fungus Fusarium oxysporum 12S (FoRham1) was cloned and characterized. FoRham1 showed the highest amino acid sequence similarity with enzymes belonging to the glycoside hydrolase (GH) family 145; however, the catalytic residue on the posterior pocket of the beta-propeller fold protein was not conserved. The catalytic residues of FoRham1 were instead conserved with ulvan lyases belonging to polysaccharide lyase (PL) family 24. Kinetic analysis showed that FoRham1 has the highest catalytic efficiency for the substrate alpha-l-rhamnose-(1-->4)-d-glucuronic acid (Rha-GlcA). The crystal structures of ligand-free and Rha-GlcA--bound FoRham1 were determined, and the active site was identified on the anterior side of the beta-propeller. The three-dimensional structure of the active site and mutagenesis analysis revealed the detailed catalytic mechanism of FoRham1. Our findings offer a new enzymatic tool for the further analysis of the GA carbohydrate structure and for elucidating its physiological functions in plants. Based on these results, we renamed GH145 as a new PL family 42, in which FoRham1 is included.

Structural and functional analysis of gum arabic l-rhamnose-alpha-1,4-d-glucuronate lyase establishes a novel polysaccharide lyase family.,Kondo T, Kichijo M, Maruta A, Nakaya M, Takenaka S, Arakawa T, Fushinobu S, Sakamoto T J Biol Chem. 2021 Jul 22:101001. doi: 10.1016/j.jbc.2021.101001. PMID:34303708^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.