Substrate specificity determinants of class III nucleotidyl cyclases

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Cyclic AMP and cyclic GMP are key signaling molecules produced by adenylyl and guanylyl cyclases, respectively.
• Accurate substrate recognition of ATP and GTP by nucleotidyl cyclases is crucial for these signaling pathways.
• Previous structural studies on guanylyl cyclases lacked information on substrate binding modes.

Purpose of the Study:

• To elucidate the structural basis of substrate selection in nucleotidyl cyclases.
• To provide atomic-level insights into the interactions between cyclases and their nucleotide substrates.
• To present the first crystallographic structures of a nucleotidyl cyclase bound to both ATP and GTP.

Main Methods:

• X-ray crystallography was used to determine the structures of the cyclase homology domain of a class III adenylyl cyclase from Mycobacterium avium (Ma1120).
• Structures were obtained for the enzyme in complex with ATP and GTP in the presence of calcium ions.
• A mutant enzyme (KDA→EGY) was also analyzed in complex with substrates.

Main Results:

• The study presents the first structures of a nucleotidyl cyclase (Ma1120 cyclase homology domain) bound to both ATP and GTP.
• Detailed atomic interactions reveal the precise mechanisms of enzyme-substrate recognition and discrimination.
• The binding pocket's ability to accommodate diverse substrate conformations was elucidated.

Conclusions:

• These findings provide a fundamental structural understanding of substrate selection by nucleotidyl cyclases.
• The presented structures offer insights into the catalytic mechanism and substrate specificity of these important enzymes.
• This work lays the groundwork for future studies on cyclase function and drug development.