Structural and Functional Perspectives of α-L-Rhamnosidase in Glycoside Biotransformation, Therapeutic Applications, and Enzyme Engineering.

α-L-Rhamnosidase is a glycoside hydrolase (GH) that cleaves α-L-rhamnosidic bonds in diverse natural substrates, including oligosaccharides, glycoproteins, flavonoids, and glycolipids that contain terminal L-rhamnose. Owing to its broad substrate specificity, it has attracted growing interest in biotechnology, food processing, pharmaceuticals, and natural product modification. Fungal and bacterial α-L-rhamnosidases show diversity in molecular architecture, catalytic efficiency, thermostability, and pH tolerance, while sharing a conserved inverting mechanism mediated by acidic residues within the GH78 and GH106 families. Structural studies reveal catalytic cores, substrate recognition motifs, and aromatic residues involved in rhamnose binding. These enzymes enable the production of bioactive compounds such as prunin, isoquercitrin, quercetin, hesperetin, icariin, and myricetin. Recent advances in computational design, protein engineering, and directed evolution have improved enzyme performance. This review summarizes the current knowledge of microbial α-L-rhamnosidases, emphasizing their sources, biochemical characteristics, substrate specificity, structural organization, catalytic mechanisms, therapeutic relevance, and recent advances in protein engineering.