A novel antimicrobial protein (AP1) was purified from leaves of the potato (Solanum tuberosum, variety MS-42.3) with a procedure involving ammonium sulphate fractionation, molecular sieve chromatography with Sephacryl S-200 and hydrophobic chromatography with Butyl-Sepharose using a FPLC system. The inhibition spectrum investigation showed that AP1 had good inhibition activity against five different strains of Ralstonia solanacearum from potato or other crops, and two fungal pathogens, Rhizoctonia solani and Alternaria solani from potato. The full-length cDNA encoding AP1 has been successfully cloned by screening a cDNA expression library of potato with an anti-AP1 antibody and RACE (rapid amplification of cDNA ends) PCR. Determination of the nucleotide sequences revealed the presence of an open reading frame encoding 343 amino acids. At the C-terminus of AP1 there is an ATP-binding domain, and the N-terminus exhibits 58% identity with an/the acid phosphatase from Mesorhizobium loti. SDS/PAGE and Western blotting analysis suggested that the AP1 gene can be successfully expressed in Escherichia coli and recognized by an antibody against AP1. Also the expressed protein showed an inhibition activity the same as original AP1 protein isolated from potato. We suggest that AP1 most likely belongs to a new group of proteins with antimicrobial characteristics in vitro and functions in relation to phosphorylation and energy metabolism of plants.

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