Complex formation between deoxyhypusine synthase and its protein substrate, the eukaryotic translation initiation...

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Deoxyhypusine synthase (DHPS) is key in hypusine biosynthesis.
• Hypusine modification is essential for the function of eukaryotic initiation factor 5A (eIF5A).
• DHPS acts on a specific protein substrate, eIF5A precursor.

Purpose of the Study:

• To investigate the stable complex formation between human DHPS and human recombinant eIF5A precursor (ec-eIF5A).
• To characterize the stoichiometry and binding affinity of the DHPS-ec-eIF5A complex.
• To understand the conditions influencing complex formation and product generation.

Main Methods:

• Affinity chromatography using polyhistidine-tagged (His.Tag) ec-eIF5A.
• Gel mobility-shift assays.
• Analytical ultracentrifugation and N-terminal amino acid sequencing.

Main Results:

• DHPS selectively bound to immobilized His.Tag-ec-eIF5A.
• A stable 1:1 complex of DHPS tetramer to ec-eIF5A monomer was identified.
• A very strong binding affinity (Kd ≤ 0.5 nM) was determined for the DHPS-ec-eIF5A interaction.
• Complex formation occurred across a pH range of 7.0-9.2 and was independent of NAD+ or spermidine.
• An enzyme-product complex and the modified eIF5A were detected under complete reaction conditions.

Conclusions:

• DHPS and ec-eIF5A form a highly stable complex with a precise 1:1 stoichiometry.
• The strong interaction facilitates the essential hypusine modification of eIF5A.
• Understanding this complex is vital for deciphering eIF5A's role in translation regulation.