Half Way to Hypusine-Structural Basis for Substrate Recognition by Human Deoxyhypusine Synthase

Area of Science:

• Biochemistry
• Structural Biology
• Molecular Biology

Background:

• Deoxyhypusine synthase (DHS) catalyzes the rate-limiting step in hypusination, a unique post-translational modification essential for cell proliferation.
• Dysregulation of hypusination is implicated in diseases like cancer and neurodegeneration.
• Understanding DHS function is critical for therapeutic development.

Purpose of the Study:

• To elucidate the high-resolution structures of human DHS in various states.
• To determine the mechanism of substrate recognition by DHS.
• To investigate the role of specific structural motifs in DHS assembly and function.

Main Methods:

• High-resolution X-ray crystallography (1.41–1.69 Å) of human DHS.
• Crystallization of apoprotein and ligand-bound states, including with spermidine (SPD).
• Enzyme activity assays and mutagenesis combined with light-scattering.

Main Results:

• Detailed structures of human DHS, including ligand-bound states, were determined.
• The mode of substrate recognition for the natural substrate spermidine (SPD) was identified.
• Polyamines spermine (SPM) and putrescine bind similarly to SPD, with SPM showing some substrate activity.
• No conformational changes were observed in DHS upon spermidine binding, contrary to previous findings.
• A conserved "ball-and-chain" motif was found to be essential for functional DHS tetramer assembly.

Conclusions:

• The study provides significant insights into DHS substrate recognition and structural dynamics.
• Findings advance the understanding of the hypusination pathway.
• The structural and mechanistic data may facilitate the design of novel therapeutic agents for cancer and neurodegenerative diseases.