ABSTRACTTwo cAMP receptor proteins (CRPs), Sycrp1 (encoded bysll1371) and Sycrp2 (encoded bysll1924), exist in the cyanobacteriumSynechocystissp. strain PCC 6803. Previous studies have demonstrated that Sycrp1 has binding affinity for cAMP and is involved in motility by regulating the formation of pili. However, the function of Sycrp2 remains unknown. Here, we report thatsycrp2disruption results in the loss of motility ofSynechocystissp. PCC 6803, and that the phenotype can be recovered by reintroducing thesycrp2gene into the genome ofsycrp2-disrupted mutants. Electron microscopy showed that thesycrp2-disrupted mutant lost the pilus apparatus on the cell surface, resulting in a lack of cell motility. Furthermore, the transcript level of thepilA9-pilA11operon (essential for cell motility and regulated by the cAMP receptor protein Sycrp1) was markedly decreased insycrp2-disrupted mutants compared with the wild-type strain. Moreover, yeast two-hybrid analysis and a pulldown assay demonstrated that Sycrp2 interacted with Sycrp1 to form a heterodimer and that Sycrp1 and Sycrp2 interacted with themselves to form homodimers. Gel mobility shift assays revealed that Sycrp1 specifically binds to the upstream region ofpilA9. Together, these findings indicate that inSynechocystissp. PCC 6803, Sycrp2 regulates the formation of pili and cell motility by interacting with Sycrp1.IMPORTANCEcAMP receptor proteins (CRPs) are widely distributed in cyanobacteria and play important roles in regulating gene expression. Although many cyanobacterial species have two cAMP receptor-like proteins, the functional links between them are unknown. Here, we found that Sycrp2 in the cyanobacteriumSynechocystissp. strain PCC 6803 is essential for twitching motility and that it interacts with Sycrp1, a known cAMP receptor protein involved with twitching motility. Our findings indicate that the two cAMP receptor-like proteins in cyanobacteria do not have functional redundancy but rather work together.
Identification and Characterization of a Novel cAMP Receptor Protein in the CyanobacteriumSynechocystissp. PCC 6803
