Structural Basis Of The Interplay Between Cytoplasmic Incompatibility Factors

Wolbachia is an intracellular symbiotic bacterium that affects about two-thirds of insects in nature.After Wolbachia infects insects,it can manipulate the host’s reproduction.The most common strategy is to induce the host cytoplasmic incompatibility（CI）.A Wolbachia infected male insect sterilizes a female unless it is infected by the same or a compatible strain,which is named unidirectional CI.In addition,CI can also form a reproductive barrier between two insect populations,if they are infected by two incompatible Wolbachia strains（bidirectional CI）.Recently,the genes involved in CI were identified.These genes,for example,cid A-cid B（cid AB）and cin A-cin B（cin AB）from Wolbachia strain w Pip and cif A-cif B（cif AB）from Wolbachia strain w Mel,form two-gene A-B systems.B has properties of a toxin（Cid B or Cif B function through deubiquitinase activity,and CinB function through nuclease activity）,while A binds B and rescues CI.However,the mechanism of how these factors specifically recognize each other and how the interactions between A and B could drive the unrivaled diversity of CI remains unknown.In this study,we mainly focused on CI factors CinA-CinB and Cid A-Cid B.The crystal structure of w Pip CinA-CinB complex was determined.It has shown that CinA belongs to a new fold structure.CinB could bind metal ions(Mn²⁺and Co²⁺)with its N-terminal nuclease active center.Using Pull-down and yeast phenotype analysis,the molecular mechanism of the interaction between CinA and CinB was revealed.Based on the crystal structure of CinA-CinB and Cid A-Cid BC（Cid B core domain）that was previously solved in our laboratory,it is found that A molecule and B molecule have a conservative interaction mode,all involving three interaction regions.In addition,we analyzed the interaction between different types of Cid A and Cid B in Wolbachia strain w Pip.Based on the above research,it has been proposed that the combination of the A molecule and the B molecule in the CI factor was essential for suppressing toxicity,and the changes of the amino acid residues in the three regions involved in the interaction can adjust the binding specificity of the A molecule and the B molecule,resulting in infection Wolbachia’s mosquitoes exhibit diverse patterns of incompatibility.These findings lay the foundation to understand the molecular mechanism behind CI,and facilitate the design of effective CI tools to control mosquito-borne diseases.