Alginate-modifying enzymes: biological roles and biotechnological uses

Abstract

Alginate denotes a group of industrially important 1-4-linked biopolymers composed of the C-5-epimers β-D-mannuronic acid (M) and α-L-guluronic acid (G). The polysaccharide is manufactured from brown algae where it constitutes the main structural cell wall polymer. The physical properties of a given alginate molecule, e.g., gel-strength, water-binding capacity, viscosity and biocompatibility, are determined by polymer length, the relative amount and distribution of G residues and the acetyl content, all of which are controlled by alginate modifying enzymes. Alginate has also been isolated from some bacteria belonging to the genera Pseudomonas and Azotobacter, and bacterially synthesized alginate may be O-acetylated at O-2 and/or O-3. Initially, alginate is synthesized as polymannuronic acid, and some M residues are subsequently epimerized to G residues. In bacteria a mannuronan C-5-epimerase (AlgG) and an alginate acetylase (AlgX) are integral parts of the protein complex necessary for alginate polymerization and export. All alginate-producing bacteria use periplasmic alginate lyases to remove alginate molecules aberrantly released to the periplasm. Alginate lyases are also produced by organisms that utilize alginate as carbon source. Most alginate-producing organisms encode more than one mannuronan C-5 epimerase, each introducing its specific pattern of G residues. Acetylation protects against further epimerization and from most alginate lyases. An enzyme from Pseudomonas syringae with alginate deacetylase activity has been reported. Functional and structural studies reveal that alginate lyases and epimerases have related enzyme mechanisms and catalytic sites. Alginate lyases are now utilized as tools for alginate characterization. Secreted epimerases have been shown to function well in vitro, and have been engineered further in order to obtain enzymes that can provide alginates with new and desired properties for use in medical and pharmaceutical applications.

Growth of theFucusembryo: insights into wall-mediated cell expansion through mechanics and transcriptomics

“…4C). To date, a number of bacterial genes encoding MC5Es have been discovered and the exact functions of some of these enzymes (their patterns of epimerization) have been investigated (76, 77). It is likely that each epimerase found here has a specific epimerization pattern and is required in different developmental stages, contributing to differential cell and tissue expansion.…”

Biphasic cellular adaptations and ecological implications of Alteromonas macleodii degrading a mixture of algal polysaccharides

“…Alginate, comprising homo-or heteropolymeric blocks of β-D-mannuronate and α-L-guluronate, can constitute >50% of benthic and pelagic brown macroalgae [47]. The environmental importance of alginate is reflected by the occurrence of alginate lyases in various bacterial taxa [48]. Pectin, largely composed of α-(1-4)-galacturonate, is abundant in terrestrial plants, but the presence of complex pectinolytic operons in marine bacteria [49] and up to 0.3 µM galacturonate during phytoplankton blooms [50] suggest that pectinous substrates are common in marine systems as well.…”

Genomics Reveals a Unique Clone of Burkholderia cenocepacia Harboring an Actively Excising Novel Genomic Island

“…In Pseudomonas aeruginosa , SGNH hydrolases are involved in acetylation of alginate, which is a long sugar polymer and the main component of Pseudomonas biofilm (Baker et al, 2014). Acetylation of alginate during its biosynthesis makes bacterial biofilm less susceptible to antibiotics, disinfectants and enable them to evade the immune system of a host (Ertesvåg, 2015). GEI also harbors gene vanY that encodes for D -alanyl- D -alanine carboxypeptidase (COG 2173) of VanY superfamily known to be involved in the cell wall biogenesis and resistance to glycopeptide antibiotic vancomycin.…”