Journal Article

Functional characterization of three Azotobacter chroococcum alginate-modifying enzymes related to the Azotobacter vinelandii AlgE mannuronan C-5-epimerase family

Brautaset, Trygve, Aarstad, Olav A., Gawin, Agnieszka, Tietze, Lisa, Aachmann, Finn L., Ertesvåg, Helga

2020

Overview

Bacterial alginate initially consists of 1–4-linked β-D-mannuronic acid residues (M) which can be later epimerized to α- L -guluronic acid (G). The family of AlgE mannuronan C-5-epimerases from Azotobacter vinelandii has been extensively studied, and three genes putatively encoding AlgE-type epimerases have recently been identified in the genome of Azotobacter chroococcum . The three A. chroococcum genes, here designated AcalgE1 , AcalgE2 and AcalgE3 , were recombinantly expressed in Escherichia coli and the gene products were partially purified. The catalytic activities of the enzymes were stimulated by the addition of calcium ions in vitro. AcAlgE1 displayed epimerase activity and was able to introduce long G-blocks in the alginate substrate, preferentially by attacking M residues next to pre-existing G residues. AcAlgE2 and AcAlgE3 were found to display lyase activities with a substrate preference toward M-alginate. AcAlgE2 solely accepted M residues in the positions − 1 and + 2 relative to the cleavage site, while AcAlgE3 could accept either M or G residues in these two positions. Both AcAlgE2 and AcAlgE3 were bifunctional and could also catalyze epimerization of M to G. Together, we demonstrate that A. chroococcum encodes three different AlgE-like alginate-modifying enzymes and the biotechnological and biological impact of these findings are discussed.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 631/337 / 631/45 / 631/61 / Alginates - chemistry / Alginates - metabolism / Alginic acid / Amino Acid Sequence / Azotobacter - chemistry / Azotobacter - enzymology / Azotobacter - genetics / Azotobacter chroococcum / Azotobacter vinelandii / Azotobacter vinelandii - chemistry / Azotobacter vinelandii - enzymology / Azotobacter vinelandii - genetics / Bacterial Proteins - chemistry / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Biocatalysis / Biotechnology / Calcium / Carbohydrate Epimerases - chemistry / Carbohydrate Epimerases - genetics / Carbohydrate Epimerases - metabolism / E coli / Enzymes / Epimerase / Genes, Bacterial / Genomes / Humanities and Social Sciences / Mannuronic acid / multidisciplinary / Multigene Family / Residues / Science / Science (multidisciplinary) / Sequence Alignment / Substrate preferences / Substrate Specificity