Mechanisms for intragenic complementation at the human argininosuccinate lyase locus

Area of Science:

• Biochemistry
• Enzymology
• Genetics

Background:

• Argininosuccinate lyase (ASL) is crucial for the urea cycle, converting argininosuccinate to arginine and fumarate.
• Deficiencies in ASL lead to argininosuccinic aciduria, an autosomal recessive disorder with variable clinical presentations.
• Intragenic complementation among ASL mutants is a key factor in the disorder's heterogeneity, but its mechanisms are poorly understood.

Purpose of the Study:

• To elucidate the molecular mechanisms of intragenic complementation in Argininosuccinate lyase (ASL).
• To investigate how different ASL mutations (active site vs. non-active site) influence complementation and enzyme function.
• To establish correlations between ASL complementation events and the clinical phenotype of argininosuccinic aciduria.

Main Methods:

• Utilized the 3-dimensional structure of wild-type ASL to hypothesize complementation mechanisms.
• Reconstructed complementation events in vivo and in vitro using recombinant proteins.
• Characterized complementation between active site mutants (Q286R, D87G) and non-active site mutants (M360T, A398D).

Main Results:

• Confirmed that complementation between ASL active site mutants (Q286R and D87G) regenerates functional active sites.
• Demonstrated that non-active site mutants (M360T, A398D) reduce ASL thermodynamic stability.
• Showed that complementation between stable (Q286R) and unstable mutants (M360T, A398D) forms a more stable heteromeric protein with partial activity recovery.
• Identified a novel complementation event between A398D and D87G mutants.

Conclusions:

• The study provides a mechanistic understanding of ASL intragenic complementation.
• Complementation can occur through active site regeneration or the formation of more stable heteromeric complexes.
• These findings offer insights into genotype-phenotype correlations in argininosuccinic aciduria, aiding clinical understanding.