Abstract
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 α-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 β-1,3-glucan synthase complex, the other being the synthase itself (Fks1), while Rho2 has been associated to the α-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 α-1,3-glucan, synthesized by Ags1p, indicated that it is essentially a linear polysaccharide, with <3% of α-1,4-linked glucose branches, occasionally attached as single units to the α-1,3-backbone.
Acknowledgements
We thank Drs Manuel Rieber, Maricela Viola and Alberto Gómez (Cellular Biochemistry Laboratory, Centro de Microbiología y Biología Celular, IVIC) for help in the densitometric image analysis of northern blots and semi-quantitative RT-PCR. We are also grateful to Dr Enrico Cabib (National Institute of Diabetes and Digestive Kidney Diseases, National Institutes of Health, Bethesda, Maryland) for the generous gift of the S. cerevisiae rho1 mutant strain used in this study. Pedro Moncada (Simón Bolívar University) and M.Sc. Sabrina Rodríguez (Laboratorio de Micología, Centro de Microbiología y Biología Celular, IVIC) ran IR spectra. This work was partially financed by ICGEB, project CRP VEN05/ 01.
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and the writing of the paper.
This paper was first published online on Early Online on 19 February 2009.