Crystal structure of LeuD from Methanococcus jannaschii

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• 3-Isopropylmalate/citramalate (IPM) isomerase is crucial for leucine biosynthesis.
• Methanococcus jannaschii IPM isomerase (MjLeuC/MjLeuD) exhibits broad substrate specificity, differing from other bacterial enzymes.
• Understanding MjLeuD's structure is key to elucidating its unique substrate recognition.

Purpose of the Study:

• Determine the crystal structure of MjLeuD to understand its broad substrate specificity.
• Identify structural features contributing to the enzyme's unique substrate recognition properties.

Main Methods:

• X-ray crystallography was used to determine the MjLeuD structure at 2.0 Å resolution.
• Analysis of the crystal structure, including homodimer formation and substrate recognition regions.

Main Results:

• The MjLeuD structure revealed a β/β/α sandwich fold with 8 α-helices and 7 β-strands.
• Conformational differences were observed in the C-terminal helix involved in homodimer formation.
• A hydrophobic residue (Val28) near the substrate recognition site was identified as a potential factor in broad substrate specificity.

Conclusions:

• The crystal structure of MjLeuD provides a molecular basis for its broad substrate specificity.
• Structural variations, including residue Val28 and homodimer conformations, contribute to MjLeuD's unique enzymatic properties.
• LeuD proteins can be classified into two subfamilies based on structural and substrate recognition differences.