Identification of β tubulin IVb as a pattern recognition receptor with opsonic activity

Previous studies have shown that tubulins play important role in immune responses of both plants and animals, but no experiments have been performed to study the mode of action of tubulins in immune defense. In addition, there is little convincing experimental evidence of functional commitment for specific tubulin isotypes in animals. In the present, we showed that expression of beta-tubulin IVb gene was affected by both LPS and LTA, hinting its involvement in anti-infectious response. We also showed that recombinant zebrafish beta-tubulin IVb not only interacted with LPS and LTA as well as Gram-negative and -positive bacteria but also agglutinated both Gramnegative and -positive bacteria in a Ca2+-dependent fashion. Interestingly, recombinant beta-tubulin IVb could enhance the phagocytosis of bacteria by macrophages. Moreover, we demonstrated that beta-tubulin IVb was present extracellularly in the serum of zebrafish and mouse. Collectively, these suggest that beta-tubulin IVb may be physiologically involved in the systematic immunity of host via acing as a pattern recognition receptor and an opsonin. This also provides a new angle to understand the roles of beta-tubulin IVb.