| Summary: | 碩士 === 國立中興大學 === 生命科學系所 === 105 === Type III secretion system is a protein appendage found in several Gram-negative bacteria. In pathogenic bacteria, the needle-like structure is used as a sensor probe to detect the presence of eukaryotic organisms and secrete proteins that help the bacteria infect them. Citrus canker is a disease affecting the bacterium species caused by the bacterium Xanthomonas axonopodis. While not harmful to humans, canker serious affects the vitality of citrus trees, causing leaves and fruit to drop prematurely. Although a fruit infected with canker is safe to eat, it will be too unsightly to be sold. The disease is caused by Xanthomonas axonopodis pv. citri (Xac) and leads to defoliation, and premature fruit drop of the citrus plant. The mechanism by which XopAI proteins cause plant bacterial ulcers is not yet known. The recombinant XopAI protein was expressed in E.coli, purified by using Ni2+ column and crystallized. The crystals belonged to space group P41212 and diffracted resolution to 1.63 Å. Because the C-terminal region of XopAI has similarity to the ADP-ribosyl transferase domains of the effector HopU1 of Pseudomonas syringae, we performed fluorescent spectroscopic analyses using three potential cofactors (NAD+, NADP+, and ADP) in order to determine the binding preference of XopAI.
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