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08:01
Sulfate Separation by Selective Crystallization with a Bis-iminoguanidinium Ligand
Published on: September 8, 2016
Channeling in sulfate activating complexes.
1The Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, New York 10461-1926, USA.
Biochemistry
|September 20, 2006
Summary
The unfavorable synthesis of activated sulfate (adenosine 5'-phosphosulfate, APS) is overcome by channeling APS between enzyme active sites. Type III sulfate activating complexes (SAC) efficiently channel APS, unlike types I and II.
Area of Science:
- Biochemistry
- Enzymology
- Molecular Biology
Background:
- The synthesis of adenosine 5 '-phosphosulfate (APS) from ATP and sulfate is thermodynamically unfavorable (Keq ≈ 10⁻⁸).
- ATP sulfurylases, catalyzing APS synthesis, exhibit significantly lower catalytic efficiency in the forward reaction compared to the reverse.
- Multifunctional complexes containing ATP sulfurylase domains may have evolved mechanisms to circumvent unfavorable energetics.
Purpose of the Study:
- To investigate whether sulfate activating complexes (SAC) can channel APS between active sites, thereby bypassing unfavorable solution-phase energetics.
- To compare APS channeling efficiency across different types of SAC from various organisms.
Main Methods:
- Development of a novel channeling assay utilizing APS reductase from Mycobacterium tuberculosis to optically detect solution-phase APS.
- Testing of type I (Homo sapiens), type II (M. tuberculosis), and type III (Rhodobacter sphaeroides) SAC for APS channeling capabilities.
- Structural modeling of type III SAC to visualize potential channeling pathways.
Main Results:
- APS channeling was not detected in type I and type II SAC.
- Type III SAC demonstrated high-efficiency APS channeling.
- Structural analysis of type III SAC revealed a 75 Å channel connecting active sites, with dynamics influenced by site occupancy.
Conclusions:
- The colocalization of sulfate activation steps within multifunctional complexes facilitates APS channeling, particularly in type III SAC.
- Intramolecular channeling provides a solution to the unfavorable energetics of APS synthesis, ensuring efficient sulfate activation.
- The identified channel in type III SAC represents a structural adaptation for efficient substrate transfer and metabolic flux.
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