Identification of bacterial guanylate cyclases

Area of Science:

• Molecular Biology
• Bacterial Physiology
• Enzymology

Background:

• The role of cyclic guanosine monophosphate (cGMP) as a bacterial second messenger remains debated.
• Distinguishing bacterial guanylate cyclases from adenylate cyclases is challenging due to sequence homology.
• Previous in vitro assays for bacterial nucleotide cyclases yielded ambiguous results.

Purpose of the Study:

• To develop a simple and reliable method for discriminating bacterial guanylate and adenylate cyclase activities.
• To functionally characterize previously identified and novel bacterial nucleotide cyclases.

Main Methods:

• Construction of a mutant cyclic adenosine monophosphate (cAMP) receptor protein (CRPG) activated by both cAMP and cGMP.
• Utilizing CRPG- and wild-type CRP-dependent lacZ gene expression in E. coli as a reporter system.
• Verification of results through direct measurement of cyclic nucleotides secreted by engineered E. coli strains.

Main Results:

• The developed genetic screen successfully differentiated guanylate cyclase activity from adenylate cyclase activity.
• Rhodospirillum centenum GcyA and Xanthomonas campestris GuaX were confirmed as primarily guanylate cyclases.
• Azospirillum sp. B510 GuaA showed guanylate cyclase activity, while Bradyrhizobium japonicum CyaA functioned as an adenylate cyclase.

Conclusions:

• The novel CRPG-based reporter system provides a robust method for identifying bacterial guanylate cyclases.
• This genetic screen facilitates the functional characterization of bacterial nucleotide cyclases.
• The developed method is expected to aid in the engineering of guanylate cyclases with specific properties.