Structure of putative tumor suppressor ALDH1L1

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Aldehyde dehydrogenase 1 family member L1 (ALDH1L1) is a putative tumor suppressor involved in folate metabolism.
• It catalyzes the NADP+-dependent conversion of 10-formyltetrahydrofolate to tetrahydrofolate and CO2.
• ALDH1L1 is a naturally fused product of three unrelated genes, forming a complex tetrameric enzyme.

Purpose of the Study:

• To elucidate the structural basis of ALDH1L1's enzymatic activity.
• To understand the domain interactions and architecture of the tetrameric enzyme.
• To investigate the role of the tetrameric state in ALDH1L1's catalytic mechanism.

Main Methods:

• Cryo-electron microscopy (Cryo-EM) to determine the structure of tetrameric rat ALDH1L1.
• Analysis of domain architecture and inter-domain interactions.
• Functional characterization of enzyme catalysis.

Main Results:

• Cryo-EM revealed the architecture of tetrameric ALDH1L1 and its functional domain interactions.
• Highly mobile N-terminal domains interact transiently.
• C-terminal aldehyde dehydrogenase domains form large interfaces with intermediate acyl/peptidyl carrier protein (A/PCP) domains.
• The 4'-phosphopantetheine arm of the intermediate domain is fully extended and accesses the catalytic pocket.
• The tetrameric state is essential for catalysis, enabling inter-protomer formyl transfer by the intermediate domain.

Conclusions:

• The tetrameric structure of ALDH1L1 is indispensable for its catalytic function in folate metabolism.
• Intermediate domains act as crucial formyl group carriers between catalytic domains of different protomers.
• These findings highlight the adaptability of A/PCP domains in complex, dynamic enzyme systems.