Specific inhibition of acid proteinase secretion inCandida albicansby Lys-Nva-FMDP

Abstract

Secretion of aspartic (acid) proteinase by Candida albicans is inhibited by the action of a new anticandidal agent, L-lysyl-l~-norvalyl-[NL(4-methoxyfumaroyl)]-L-Z3-diaminopropanoic acid (Lys-Nva-FMDP), at low, even sub-minimum inhibitory concentrations. The observed phenomenon is a direct consequence of inhibition of the enzyme, glucosamine-6-phosphate synthase. As a result of this inhibition, biosynthesis of candidal mannoproteins is markedly reduced. A possible correlation between general inhibition of mannoprotein biosynthesis and acid proteinase secretion is suggested. The reported inhibition of acid proteinase secretion by Lys-Nva-FMDP is more specific than the previously described effects of methyl patricim 5-fluorocytosine and fenticonazole.The secretory aspartic proteinase of Candida albicans is generally considered to be a virulence factor of this opportunistic pathogen [22,30]. Secretion of proteinase was found to be correlated with other virulence properties of C. albicans cells, such as adherence [11]. In light of recent reports, the physiological role of this enzyme during colonization of the host organism by the fungus is thought to be: (i) degradation of skin and mucosal barriers which augments the adherence of fungal cells to host tissues [4,14,16]: (ii) digestion of host proteins in order to supply nutrients [20]; and (iii) breaking the immune barrier by attacking lymphocytes and macrophages [11,22]. Therefore, antimycotics able to inhibit either acid proteinase activity or its secretion should be considered as especially valuable potential anticandidal drugs. Such a phenomenon has been observed for methyl patricin, 5-fluorocytosine and fenticonazole, but not for other antifungal azoles [3]. On the other hand, pepstatin, a selective inhibitor of aspartic proteases, given parenterally proved effective against systemic murine candidosis [33].Antifungal properties of rationally designed synthetic oligopeptides containing N-(4-methoxytumaroyl)-L-2,3-dlamlnopropanolc acid (FMDP) residue have recently been described [1,2]. These compounds were shown to be chemotherapeutically effective anti-candidal agents in the model of generalized candidosis in mice [25]. Studies on the mechanism of action of FMDP-peptides revealed that they were transported into C. albicans cells by peptide permeases and cleaved by intracellular peptidases; the released FMDP selectively inactivated the enzyme, glucosamine-6-phosphate (GlcN-6-P) synthase [23]. The shortage of the biosynthetic glucosamine resulted in inhibition of biosynthesis of glucosamine-containing cell wall macromolecules: chitin and mannoprotein [23]. Previously, we showed that inhibition of GlcN-6-P synthase resulted in decreased secretion of two glycoprotein secretory enzymes: invertase and

Enzymes of UDP‐GlcNAc biosynthesis in yeast

“…On the other hand, gene deletion or inhibition of the respective enzyme of the Leloir pathway is likely to affect the virulence, surface properties and adherence of fungal cells, as was shown in studies concerning C. albicans GlcN‐6‐P synthase and GlcN‐6‐P acetyltransferase 56, 67. This phenomenon, as well as the observed inhibition of secretion of several extracellular enzymes, including aspartic protease, in C. albicans cells treated with GlcN‐6‐P synthase inhibitors,59 should most likely be attributed to the inhibition of N ‐glycosylation of secretory enzymatic and cell wall mannoproteins.…”

Secreted aspartic proteases of Candida albicans, Candida tropicalis, Candida parapsilosis and Candida lusitaniae

“…Novel pepstatin‐like inhibitors isolated from Streptomyces sp. [63,64] were not as efficient as pepstatin A. Secretion of Sap of C. albicans was efficiently inhibited by Lys‐Nva‐FMDP [65]. A series of hexapeptides with hydroxyethylene isostere (A‐70450 analogs) was tested for the inhibition of Sap2p [22].…”

Cell Wall and Secreted Proteins ofCandida albicans: Identification, Function, and Expression

“…A 45-kDa intracellular form of the secretory aspartyl proteinase that seems to be the precursor of the 43-kDa mature enzyme has been reported (205,206). It has been suggested that although the mature form is not glycosylated, that glycosylation may occur to some extent in the 45-kDa precursor (353), which may partly explain the results reported by Akashi et al (3).…”