Acaconin, a chitinase-like antifungal protein with cytotoxic and anti-HIV-1 reverse transcriptase activities from Acacia confusa seeds

From the seeds of Acacia confusa, a chitinase-like antifungal protein designated as acaconin that demonstrated antifungal activity toward Rhizoctonia solani with an IC50 of 30 +/- 4 mu M was isolated. Acaconin demonstrated an N-terminal sequence with pronounced similarity to chitinases and a molecular mass of 32 kDa. It was isolated by chromatography on Q-Sepharose, SP-Sepharose and Superdex 75 and was not bound by either ion exchanger. Acaconin was devoid of chitinase activity. The antifungal activity against Rhizoctonia solani was completely preserved from pH 4 to 10 and from 0 degrees C to 70 degrees C. Congo Red staining at the tips of R. solani hyphae indicated inhibition of fungal growth. However, there was no antifungal activity toward Mycosphaerella arachidicola, Fusarium oxysporum, Helminthosporium maydis, and Valsa mali. Acaconin inhibited proliferation of breast cancer MCF-7 cells with an IC50 of 128 +/- 9 mu M but did not affect hepatoma HepG2 cells. Its IC50 value toward HIV-1 reverse transcriptase was 10 +/- 2.3 mu M. The unique features of acaconin include relatively high stability when exposed to changes in ambient pH and temperature, specific antifungal and antitumor actions, potent HIV-reverse transcriptase inhibitory activity, and lack of binding by strongly cationic and anionic exchangers.