Structures and function of the amino acid polymerase cyanophycin synthetase

Cyanophycin is a natural biopolymer produced by a wide range of bacteria, consisting of a chain of poly-l-Asp residues with l-Arg residues attached to the beta-carboxylate sidechains by isopeptide bonds. Cyanophycin is synthesized from ATP, aspartic acid and arginine by a homooligomeric enzyme called cyanophycin synthetase (CphA1). CphA1 has domains that are homologous to glutathione synthetases and muramyl ligases, but no other structural information has been available. Here, we present cryo-electron microscopy and X-ray crystallography structures of cyanophycin synthetases from three different bacteria, including cocomplex structures of CphA1 with ATP and cyanophycin polymer analogs at 2.6 angstrom resolution. These structures reveal two distinct tetrameric architectures, show the configuration of active sites and polymer-binding regions, indicate dynamic conformational changes and afford insight into catalytic mechanism. Accompanying biochemical interrogation of substrate binding sites, catalytic centers and oligomerization interfaces combine with the structures to provide a holistic understanding of cyanophycin biosynthesis.

Automated summary

This study presents cryo-electron microscopy and X-ray crystallography structures of cyanophycin synthetases from three different bacteria, including cocomplex structures of CphA1 with ATP and cyanophycin polymer analogs at 2.6 angstrom resolution. These structures reveal two distinct tetrameric architectures, show the configuration of active sites and polymer-binding regions, indicate dynamic conformational changes, and afford insight into catalytic mechanism. Accompanying biochemical interrogation of substrate binding sites, catalytic centers, and oligomerization interfaces combine with the structures to provide a holistic understanding of cyanophycin biosynthesis.