Structural analysis of molybdopterin synthases from two mycobacterial pathogens

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Molybdenum cofactor (Moco) is essential for molybdenum enzyme activity.
• Moco biosynthesis involves multiple enzymatic steps, with molybdopterin synthase catalyzing a key reaction.
• Mycobacteria possess diverse genes for Moco biosynthesis, including homologs in M. tuberculosis.

Purpose of the Study:

• To elucidate the structural basis of molybdopterin synthase function in mycobacterial pathogens.
• To compare the structures of M. tuberculosis and M. smegmatis molybdopterin synthases.
• To identify potential targets for novel antimycobacterial agents.

Main Methods:

• X-ray crystallography was used to determine the structures of substrate-free molybdopterin synthases.
• Purified enzymes from M. tuberculosis and M. smegmatis were crystallized.
• Structures were resolved at 2.1 Å (M. tuberculosis) and 2.6 Å (M. smegmatis) resolutions.

Main Results:

• The crystal structures revealed hetero-tetrameric complexes of molybdopterin synthase (MoaE2 dimer with flanking MoaD2 subunits).
• The active site pocket is formed by the insertion of the MoaD2 carboxyl-terminal domain into MoaE2.
• Conserved substrate-binding and catalytic residues were identified despite low sequence similarity.
• Low sequence identity at the MoaE-MoaD interface was observed.

Conclusions:

• The determined structures provide insights into the conserved mechanism of molybdopterin synthase in mycobacteria.
• Conserved active site residues suggest a common catalytic strategy across different mycobacterial species.
• The structural differences at the heterodimer interface present a potential avenue for developing specific mycobacterial inhibitors.