HadBD dehydratase from Mycobacterium tuberculosis fatty acid synthase type II: A singular structure for a unique...

Area of Science:

• Biochemistry and Molecular Biology
• Microbiology and Infectious Diseases
• Structural Biology

Background:

• Tuberculosis (TB) remains a major global infectious killer, with multidrug resistance complicating treatment.
• Mycolic acids are essential lipids for Mycobacterium tuberculosis (Mtb) survival, virulence, and persistence.
• Enzymes in mycolic acid biosynthesis are key drug targets; HadD was previously implicated in ketomycolic acid production and virulence.

Purpose of the Study:

• To elucidate the functional role and quaternary structure of the (3R)-hydroxyacyl-ACP dehydratase (HAD) enzyme involved in mycolic acid biosynthesis in Mtb.
• To investigate the interaction between HadD and HadB proteins and their contribution to enzyme activity and substrate specificity.
• To provide structural insights into the HadBD complex for the development of novel anti-TB therapeutics.

Main Methods:

• Biochemical assays to determine enzyme activity and subunit interactions.
• X-ray crystallography to determine the 3D structure of the HadBD_Mtb complex.
• Computational modeling and cell-based analyses to understand substrate binding and structure-function relationships.

Main Results:

• The catalytically active form of the HAD enzyme is a heterotetramer composed of HadB (catalytic subunit) and HadD (substrate-binding subunit).
• Structural analysis revealed unique features of HadD, including a flexible substrate-binding crevice and a truncated hotdog fold, enabling specificity for ultra-long-chain lipids.
• HadBD_Mtb, not HadD alone, represents the biologically relevant functional unit for mycolic acid biosynthesis.

Conclusions:

• The functional unit for mycolic acid biosynthesis in Mtb is the HadBD heterotetramer, highlighting a complex assembly previously uncharacterized.
• Understanding the structure and function of the HadBD complex is critical for targeting mycolic acid synthesis.
• These findings pave the way for designing innovative antivirulence strategies by targeting the entire HadBD complex rather than individual subunits.