Molecular mechanism underlying promiscuous polyamine recognition by spermidine acetyltransferase

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Spermidine acetyltransferase (SAT) regulates polyamine levels in prokaryotes.
• Understanding SAT's structure and function is crucial for comprehending polyamine metabolism.

Purpose of the Study:

• To determine the crystal structure of Escherichia coli SAT in complex with substrates.
• To elucidate the structural basis for SAT's enzymatic activity and substrate specificity.

Main Methods:

• X-ray crystallography at 2.5Å resolution.
• Structure-based mutagenesis.
• In-vitro enzymatic assays.

Main Results:

• The crystal structure of SAT as a dodecamer (hexamer of dimers) complexed with spermidine (SPD) and CoA was determined.
• SAT shares structural similarities with SSAT, suggesting an evolutionary link, but exhibits distinct promiscuous polyamine specificity.
• A deep, acidic, water-filled cavity houses the SPD and CoA binding sites, with key residues identified through mutagenesis.

Conclusions:

• The study provides insights into the acetylation mechanism of SAT, highlighting the role of acidic residues in substrate binding and activity.
• The findings suggest a potential evolutionary relationship between SAT and SSAT.
• SAT's promiscuous polyamine recognition mechanism is elucidated through structural and functional data.