Plant biomass is one of the most abundant renewable resources on Earth. Agricultural waste such as sugarcane bagasse, wheat straw, and wood residues contains lignocellulose, the main component of plant cell walls. Lignocellulose is composed of three primary parts: cellulose, hemicellulose, and lignin. Because it is rich in polysaccharides, this biomass has the potential to be used as a raw material for producing fermentable sugars that can be applied in various biotechnological processes, including biofuel production.

However, the structure of lignocellulose is highly complex, making it difficult to break down. Hemicellulose, one of its key components, has a branched structure composed of various types of sugars. One common form of hemicellulose found in cereal plants is arabinoxylan. This molecule consists of a xylose backbone decorated with arabinose sugar branches and other chemical groups. These branched structures can hinder the activity of enzymes responsible for breaking down the main chain.

To overcome this barrier, specialized enzymes are needed to remove arabinose branches from hemicellulose. One such enzyme is known as α-L-arabinofuranosidase (AF). This enzyme works by cleaving the bonds that connect arabinose to the polysaccharide chain. As these branches are reduced, other enzymes can more easily access and degrade the hemicellulose structure.

A study reported the characterization of a new α-L-arabinofuranosidase enzyme from the bacterium Paenibacillus antarcticus. This bacterium is psychrotolerant, meaning it can survive at relatively low temperatures, and was originally discovered in Antarctic environments. The gene encoding this enzyme was identified in the bacterial genome and then recombinantly expressed in Escherichia coli. The expressed enzyme was named rPan-AF51.

Based on sequence and structural analysis, rPan-AF51 belongs to the glycoside hydrolase family 51 (GH51). Biochemical testing showed that this enzyme has optimal activity at around pH 6.0 and a temperature of approximately 35°C. In addition, it is relatively stable across a fairly wide pH range, from pH 6 to pH 10. Its activity can still be detected at lower temperatures, consistent with the cold-adapted nature of its source bacterium.

The study also found that the activity of rPan-AF51 is sensitive to certain transition metal ions and detergents, but relatively unaffected by some main-group metal ions and additives such as EDTA, β-mercaptoethanol, and ethanol. Furthermore, the presence of monosaccharides does not strongly inhibit the enzyme’s activity.

From a catalytic standpoint, rPan-AF51 is an exo-acting enzyme, meaning it cleaves arabinose units from the ends of polysaccharide chains. It is capable of hydrolyzing several types of arabinofuranoside linkages, including α-1,2, α-1,3, and α-1,5 bonds in arabinose-containing substrates. This ability indicates that the enzyme has relatively broad substrate specificity.

An important aspect examined in this study is the interaction between rPan-AF51 and other enzymes involved in hemicellulose degradation. When rPan-AF51 is used together with β-xylanase and β-xylosidase, there is an enhancement in the breakdown of natural arabinoxylan into simpler sugars. This demonstrates a synergistic effect among these enzymes in the saccharification process of hemicellulose.

These findings provide additional insight into the diversity of enzymes involved in plant biomass degradation. The characteristics of rPan-AF51—including its ability to function at low to moderate temperatures and to cleave various types of arabinose linkages—may serve as a basis for further research on enzyme applications in biomass bioconversion processes.

In addition, this study represents the first report on the characterization of an enzyme from Paenibacillus antarcticus. The results highlight that microorganisms living in extreme environments can serve as valuable sources of enzymes with diverse biochemical properties, which can be further explored in biotechnology research.

Author: Ali Rohman, PhD

The original article was published by Elsevier in the journal Biocatalysis and Agricultural Biotechnology and can be accessed at:
https://www.sciencedirect.com/science/article/pii/S1878818126000095

This article is a repost from the Popular Scientific Articles page of Universitas Airlangga (UNAIR) and has been adapted for publication on the Chemistry UNAIR page. Original source: “Enzymes from Antarctic Bacteria that Help Break Down Plant Biomass”