Structural basis for monolignol oxidation by a maize laccase.

Area of Science:

• Biochemistry
• Plant Biology
• Structural Biology

Background:

• Plant laccases catalyze monolignol oxidation during lignification, a vital process for plant cell wall structure and defense.
• Lignification provides mechanical support, aids nutrient transport, and protects plants against pathogens.
• Isozymes of plant laccases exhibit diverse substrate preferences, necessitating detailed characterization of individual enzymes.

Purpose of the Study:

• To characterize the substrate preference of a laccase (ZmLac3) from Zea mays (maize).
• To elucidate the structural basis for the substrate binding and orientation of ZmLac3.
• To provide insights into ZmLac3 catalysis for potential industrial applications.

Main Methods:

• X-ray crystallography was used to determine the crystal structure of ZmLac3.
• The binding modes of sinapyl alcohol (SinA) and coniferyl alcohol (ConA) to ZmLac3 were solved.
• Kinetic analysis was performed to understand enzyme-substrate interactions.

Main Results:

• The crystal structure of ZmLac3 revealed a compact and deep substrate-binding pocket.
• The binding pocket features a regionalization of polar and hydrophobic surfaces, crucial for orienting SinA and ConA.
• An additional methoxyl group in SinA significantly enhances interactions with ZmLac3 compared to ConA.

Conclusions:

• Polar and hydrophobic interactions within the ZmLac3 binding pocket dictate the binding positions of monolignols.
• Understanding these interactions provides valuable insights into ZmLac3's catalytic mechanism.
• The findings can aid in optimizing industrial processes utilizing plant laccases.