Hyphal Morphology and Elongation Alterations in <i>Aspergillus nidulans</i> Provoked by the Diterpene Kaurenoic Acid

Abstract

Kaurenoic acid (KA), a kaurane-type diterpene extracted from leaves of Mikania hirsutissima, was previously reported as an inhibitor of vascular contractility mainly by blocking extracellular Ca 2+ influx. The compound is known for several other biological activities such as antiparasitic, antispasmodic and antibacterial activity. The aim of the present study was to investigate the effect of KA on Aspergillus nidulans. KA (0.3 mM) showed fungistatic activity against A. nidulans with visible hyphal elongation and morphology damage. These effects were reverted by CaCl 2 addition showing that KA interferes with intracellular Ca 2+ gradient in A. nidulans. This is the first report on the mechanism of action of KA involving calcium levels by altering the elongation of fungi hyphae.

Methyl and p-Bromobenzyl Esters of Hydrogenated Kaurenoic Acid for Controlling Anthracnose in Common Bean Plants

“…However, for kaurenoic acid ( 1 ) the calculations obtained from the computational programs Plants, Autodock, and Paradocks, indicated very low affinities of this substance for the enzymes, suggesting that this compound does not act against fungi by inhibiting their KSIs. This result seems to be consistent with the previously demonstrated association between the antifungal activity of compound 1 and its ability to interfere with the intracellular Ca 2+ gradient in fungal cells …”

“…A similar situation was observed for substance 7 , for which many of the hydrophobic interactions with the enzyme were more similar to those observed for substance 9 . Even kaurenoic acid, 1 , − presented no clear polar interaction of its carboxylate ion with the amino acid residues of the enzyme, which may explain the lower calculated binding affinity for this substance. These results suggest that replacing the carboxylate group of 9 with a less polar functional group between the p -bromobenzyl group and the diterpene ring should increase the binding affinity.…”

“…Although more than 60 tridimensional structures of KSIs have been deposited in the RCSB protein data bank, only a few have no missing residues or atoms close to the active site, or mutations that can interfere with their biological activity. Therefore, only those enzyme structures that did not present with either of these problems were selected for molecular docking, which was carried out with both diastereoisomers of compounds 7 ( 7 - S and 7 - R ) and 9 ( 9 - S and 9 - R ), inhibitors of KSIs ( 17 – 24 ), and antifungal substances ( 1 and 25 – 30 ) ,,− with chemical structures similar to 7 or 9 (Figure ). Although the results obtained from the four computer programs used for molecular docking did not completely agree (Figure ), there was no significant difference observed between the diastereoisomers of compounds 7 or 9 , suggesting that both of these present the same biological activity.…”

“…This result seems to be consistent with the previously demonstrated association between the antifungal activity of compound 1 and its ability to interfere with the intracellular Ca 2+ gradient in fungal cells. 7 It appeared that the affinities of the substances tested for amino acid residues in the active sites of KSIs were predominantly hydrophobic interactions, as can be exemplified by substance 9. The oxygen atoms of the carboxyl group did not even form hydrogen bonds with the amino acid residues of the enzyme.…”

“…6 One possibility to circumvent the problems associated with the use of commercial fungicides is the development of naturally derived substances as fungicides. Kaurenoic acid appears to be an interesting starting point, as it has demonstrated in vitro activity against the fungi Aspergillus nidulans G. Winter, 7 Sclerotinium sclerotiorum (Lib.) de Bary, Verticillium dahlia Kleb., 8 Trichophyton rubrum (Castell.)…”