Structure and function of a hexameric cyanophycin synthetase 2.

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Cyanophycin is a nitrogen-storage biopolymer with industrial potential.
• Cyanophycin synthetase 2 (CphA2) synthesizes cyanophycin from a dipeptide precursor.
• CphA2 exists in various oligomeric states, with limited structural data available.

Purpose of the Study:

• To determine the cryo-EM structure of hexameric CphA2.
• To elucidate substrate-binding interactions and the role of oligomerization in CphA2 activity.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to resolve CphA2 structures.
• Site-directed mutagenesis to investigate residue function.
• Biochemical assays to assess enzyme activity.

Main Results:

• Reported cryo-EM structures of hexameric CphA2 at ~2.8 Å resolution.
• Identified a trimer-of-dimers hexameric architecture with substrate-binding sites similar to CphA1.
• Demonstrated that hexamerization enhances cyanophycin synthesis rates.

Conclusions:

• The study provides high-resolution structures of CphA2, revealing its hexameric assembly and substrate interactions.
• Conserved residues are crucial for substrate binding, and hexamerization is essential for efficient cyanophycin production.
• Enhanced mechanistic understanding of this industrially relevant biopolymer's biosynthesis.