Alginate modifying enzymes: An updated comprehensive review of the mannuronan C5-epimerases

Alginate is a linear polysaccharide composed of β-D-mannuronate (M) and α-L-guluronate (G). Alginate and its degradation products (alginate oligosaccharides) possess abundant biological activities such as antitumor activity and antimicrobial activity, which have great application value in food, pharmaceutical, and agricultural fields. The M/G ratio of alginate determine its biological activity and physicochemical properties. Mannuronan C5-epimerases can catalyze the conversion of β-D-mannuronate (M) to its C5 epimer α-L-guluronate (G) in vitro. With the development of technology, the number of mannuronan C5-epimerases characterized gradually increased. As the main mannuronan C5-epimerases, the properties, catalytic mechanisms and structures of AlgE-type and AlgG-type enzymes have been reported. The potential applications of mannuronan C5-epimerases on tailored alginate have also been explored. Modification engineering helps to improve the properties of mannuronan C5-epimerases, thus making it possible to tailor alginate in vitro. This comprehensive information should be helpful to expand the research and application of mannuronan C5-epimerases.