Molecular determinants for substrate selectivity of ω-transaminases

Area of Science:

• Biochemistry
• Enzymology
• Protein Engineering

Background:

• Omega-transaminases (ω-TAs) are crucial industrial enzymes for producing chiral amines.
• Existing ω-TAs display highly similar substrate selectivity, limiting the synthesis of diverse chiral amines.
• This selectivity is characterized by steric constraints in the small (S) pocket and dual recognition in the large (L) pocket.

Purpose of the Study:

• To clone, purify, and characterize novel ω-TAs from Ochrobactrum anthropi, Acinetobacter baumannii, and Acetobacter pasteurianus.
• To investigate the molecular determinants responsible for the conserved substrate specificity among ω-TAs.
• To explore the potential for engineering ω-TAs for broader substrate acceptance.

Main Methods:

• BLASTP search to identify potential ω-TA candidates.
• Gene cloning, protein purification, and enzyme characterization.
• Molecular docking simulations using the X-ray structure of a Pseudomonas putida ω-TA to identify key active site residues.

Main Results:

• Three new ω-TAs were successfully cloned, purified, and characterized, confirming their enzymatic activity.
• All newly identified ω-TAs demonstrated substrate specificity similar to previously known enzymes.
• Docking simulations revealed conserved key residues (Tyr23, Phe88, Tyr152, Arg414, Trp60, Ile262) in the active site responsible for substrate binding and selectivity.

Conclusions:

• The high similarity in substrate selectivity among ω-TAs is attributed to conserved active site residues.
• The identified key residues dictate the steric limitations of the S pocket and the recognition mechanisms of the L pocket.
• Understanding these molecular determinants is essential for future protein engineering efforts to expand the substrate scope of ω-TAs.