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, which is the main component of plant cell walls. Lignocellulose consists of three major components: cellulose, hemicellulose, and lignin. Due to its richness in polysaccharides, this biomass has the potential to be utilized as a raw material for producing fermentable sugars that can be used in various biotechnology processes, including biofuel production.
However, the structure of lignocellulose is highly complex and difficult to break down. Hemicellulose, one of its important 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 xylosyl backbone decorated with arabinose branches and other chemical groups. These branched structures can hinder the action of enzymes responsible for breaking down the main chain.
To overcome this obstacle, a specific enzyme capable of removing arabinose branches from hemicellulose is required. This enzyme is known as α-L-arabinofuranosidase (AF). It works by cleaving the bonds connecting 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 novel 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 the Antarctic environment. The gene encoding the enzyme was identified in the bacterial genome and subsequently expressed recombinantly in Escherichia coli. The resulting expressed enzyme was named rPan-AF51.
Based on sequence and structural analyses, rPan-AF51 belongs to the glycoside hydrolase family 51 (GH51). Biochemical testing showed that this enzyme has optimal activity at approximately pH 6.0 and a temperature of around 35 °C. In addition, the enzyme is relatively stable across a broad pH range, from pH 6 to pH 10. Enzyme activity was still detectable at lower temperatures, consistent with the cold-adapted characteristics of its source bacterium.
The study also demonstrated that the activity of rPan-AF51 is sensitive to several transition metal ions and detergents but is relatively unaffected by certain main-group metal ions and additives such as EDTA, β-mercaptoethanol, and ethanol. Furthermore, the presence of monosaccharides did not strongly inhibit enzyme activity.
From the catalytic perspective, rPan-AF51 is an exo-acting enzyme, meaning that it cleaves arabinose groups from the ends of polysaccharide chains. The enzyme is capable of hydrolyzing several types of arabinofuranoside bonds, including α-1,2, α-1,3, and α-1,5 linkages in arabinose-containing substrates. This capability indicates that the enzyme has relatively broad substrate specificity.
One important aspect observed in this study was the interaction of rPan-AF51 with other enzymes involved in hemicellulose degradation. When rPan-AF51 was used together with β-xylanase and β-xylosidase enzymes, the breakdown of natural arabinoxylan into simpler sugars increased. This finding demonstrates a synergistic effect among these enzymes in the hemicellulose saccharification process.
These findings provide additional information regarding 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 its capability to cleave several types of arabinose linkages, may serve as a foundation for further research on the utilization of enzymes in biomass bioconversion processes.
In addition, this study is the first report on the characterization of an enzyme from Paenibacillus antarcticus. The results demonstrate that microorganisms living in extreme environments can become sources of enzymes with diverse biochemical properties that can still 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 via: https://www.sciencedirect.com/science/article/pii/S1878818126000095
This article is reposted from the Popular Scientific Article page of Universitas Airlangga (UNAIR) and has been adapted for publication on the Chemistry UNAIR website.
Original source: “Enzim dari Bakteri Antartika yang Membantu Mengurai Biomassa Tumbuhan”
