Recombinant E.coli cyaA protein

CyaA, or adenylate cyclase toxin, is a key virulence factor produced by *Bordetella pertussis*, the bacterium responsible for whooping cough. This multifunctional protein belongs to the RTX (Repeats in ToXin) toxin family and plays a dual role in bacterial pathogenesis. First, it penetrates host immune cells (primarily phagocytes) using a calcium-dependent mechanism, where its N-terminal adenylate cyclase domain converts cellular ATP into excessive cyclic AMP (cAMP). This disrupts host cell signaling, suppressing immune responses and promoting bacterial survival. Second, CyaA acts as a hemolysin, lysing red blood cells through pore formation.

Recombinant CyaA (rCyaA) has been engineered for research and therapeutic applications. By deleting or mutating its enzymatic domain while retaining its cell-penetrating capacity, scientists created a detoxified yet immunogenic carrier. This modified version serves as a potent antigen delivery platform, capable of shuttling heterologous antigens into antigen-presenting cells to stimulate robust CD8+ T-cell and antibody responses. Its unique ability to access the cytosolic MHC-I pathway makes it valuable for vaccine development, particularly for intracellular pathogens and cancer immunotherapy.

Recent studies highlight rCyaA's versatility. In preclinical models, it has been used to deliver tumor-associated antigens, viral epitopes, and autoimmune disease targets. The protein's built-in adjuvant properties, derived from its interaction with host cell receptors like αMβ2 integrin, enhance immune activation without requiring additional adjuvants. Additionally, structural studies of rCyaA have advanced our understanding of RTX toxin membrane insertion mechanisms, informing both basic microbiology and biotechnological applications. Current challenges include optimizing antigen-loading efficiency and balancing immunogenicity with safety in clinical translation.