Cell wall glucan synthases and GTPases in Paracoccidioides brasiliensis.

In this report we identified orthologues of fungal AGS1, RHO1, RHO2, RAC1 and CDC42 genes in the dimorphic fungus Paracoccidioides brasiliensis. Based on its homology to known fungal sequences, P. brasiliensis Ags1 was identified as an alpha-1,3-glucan synthase, while Rho1, Rho2, Rac1 and Cdc42 proteins were classified into the Rho1, Rho2, Rac1 and Cdc42 subgroups of fungal Rho GTPases, respectively. Of them, Rho1 is one of two subunits of a putative beta-1,3-glucan synthase complex, the other being the synthase itself (Fks1), while Rho2 has been associated to the alpha-1,3-glucan synthase (Ags1). Expression studies showed that mRNAs levels of RHO2 and AGS1 kept a direct relationship but the levels of RHO1 and FKS1 did not. P. brasiliensis RHO1 successfully restored growth of Saccharomyces cerevisiae rho1 mutant under restrictive temperature conditions. Chemical analyses of P. brasiliensis alpha-1,3-glucan, synthesized by Ags1p, indicated that it is essentially a linear polysaccharide, with <3% of alpha-1,4-linked glucose branches, occasionally attached as single units to the alpha-1,3-backbone.