C-terminal loop of Streptomyces phospholipase D has multiple functional roles

Area of Science:

• Biochemistry
• Enzymology
• Microbial Biotechnology

Background:

• Streptomyces phospholipase D (PLD) enzymes play crucial roles in cellular processes.
• Previous studies identified Gly188 and Asp191 in Streptomyces septatus TH-2 PLD (TH-2PLD) as critical for phospholipid recognition.
• The function of other regions, particularly the C-terminal loop, in TH-2PLD activity remained less understood.

Purpose of the Study:

• To elucidate the role of the C-terminal flexible loop of TH-2PLD in its catalytic mechanism and substrate recognition.
• To identify specific amino acid residues within this loop that influence PLD activity.
• To engineer a more robust and efficient TH-2PLD variant.

Main Methods:

• Construction and analysis of chimeric and mutant TH-2PLD enzymes.
• Assays measuring hydrolytic and transphosphatidylation activities.
• Characterization of mutant enzyme properties including thermostability and solvent tolerance.
• Site-directed mutagenesis substituting Ala426 with Phe and Lys438 with His.

Main Results:

• Residues Ala426 and Lys438 in the C-terminal loop were identified as key determinants of TH-2PLD hydrolytic and transphosphatidylation activities.
• Unlike Gly188 and Asp191 which recognize substrate forms, Ala426 and Lys438 enhance activity irrespective of substrate form.
• Mutating Ala426 to Phe and Lys438 to His resulted in enhanced enzyme activity, increased thermostability, and improved tolerance to organic solvents.
• The engineered mutant exhibited enhanced selectivity in transphosphatidylation reactions.
• These functional residues are located in a flexible C-terminal loop, separate from conserved catalytic motifs, acting as the active well entrance.

Conclusions:

• The C-terminal flexible loop of Streptomyces PLD, specifically residues Ala426 and Lys438, plays a significant, multi-faceted role in enzyme catalysis and substrate interaction.
• Engineering these residues can lead to improved enzyme properties, including enhanced activity, stability, and selectivity.
• This study provides insights into the reaction mechanism and substrate recognition of Streptomyces PLD, offering potential for biotechnological applications.