Endopolygalacturonases reveal molecular features for processivity pattern and tolerance towards acetylated pectin

Area of Science:

• Biochemistry
• Enzymology
• Molecular Biology

Background:

• Pectin, a complex polysaccharide, is hydrolyzed by endopolygalacturonases (EndoPGs).
• EndoPG activity is influenced by pectin's degree of methyl and acetyl esterification.
• Understanding enzyme specificity is crucial for pectin modification applications.

Purpose of the Study:

• To elucidate the molecular basis of substrate tolerance and processivity in three distinct EndoPGs.
• To identify key amino acid residues responsible for differential substrate binding and catalytic activity.
• To explain the distinct hydrolytic mechanisms of EndoPGs from Aspergillus niger (AnPGI, AnPGII) and Fusarium moniliforme (FmPG) on acetylated pectin.

Main Methods:

• Bioinformatics and molecular modeling techniques were employed.
• In silico modeling of homogalacturonan fragments complexed with the three EndoPGs.
• Docking pattern analysis and identification of substrate-binding amino acid residues.
• Normal mode analysis to compute enzyme motion and predict processivity.

Main Results:

• Distinct substrate tolerance profiles and processivity schemes were revealed for AnPGI, AnPGII, and FmPG.
• Key amino acid residues (e.g., S191(An)(PGI)/D240(An)(PGI) in AnPGI) were identified as crucial for pectin backbone binding and specificity.
• AnPGI exhibits a shear bending motion facilitating processive hydrolysis, while AnPGII and FmPG show hinge binding motions limiting activity.

Conclusions:

• The study provides molecular-level insights into the differential activity of EndoPGs on acetylated pectin.
• Specific amino acid residues dictate the specificity and processivity of these enzymes.
• Findings contribute to understanding pectin structure-function relationships and enzyme engineering for industrial applications.