Study of disturbance mechanisms of maintenance of fungal cell walls mediated by abnormal sterols.

Author(s)

Leydi Roxana Gutiérrez Armijos

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Ciências Biomédicas (ICB/SDI)
• Defense date: 2019-07-26

Examining board members

Agustín Hernández López; Gabriel Padilla Maldonado; Carla Columbano de Oliveira; Anita Hilda Straus Takahashi

• Advisor: Agustín Hernández López

Abstract

In both plants and fungi it is known the relation between defects in sterol homeostasis and fragility of the cell wall. For example, in fungi, mutations in the late steps of the ergosterol biosynthesis pathway or treatment with Sterol Biosynthesis Inhibitors (SBI fungicides) results in such fragility. The mechanism for this phenomenon is still unknown, although it is of capital importance to understand the fungistatic effects of these medical and agricultural important compounds, as well as the involvement of lipids in the regulation of biological processes. Previously, our group reported that 8-dehydrosterols inhibit V-ATPase activity in vivo, with negative consequences for endocytosis and normal localization of Pma1p, a plasma membrane protein, which was relocated partially to the vacuole. This prompted us to think that accumulation of abnormal sterols may be affecting cell wall biosynthesis through either an inhibitory lipid-protein interaction or through mislocalization of membrane proteins. The first candidate proteins to consider likely to be affected would be those responsible for the synthesis of cell wall polymers, particularly Fks1p (the main glucan synthase) since glucan is the major polymer in the cell wall. Mutants in the ERG2 gene showed reduced levels of glucan in their cell walls concomitant with a smaller glucan synthase activity in whole cell extracts. Particularly, in a W303-1a-derived GAL1promERG2 conditional mutant grown on glucose media (akin to a fungicide-treated fungal cell), a reduction in the glucan synthase Vmax was clear. Similarly, Fks1p protein levels showed a decrease in erg2- mutants, with a drop similar in extent to that observed in the Vmax. However, no alteration in the activity of the CWI signalling pathway was observed. Data on the location of Fks1p in wild-type cells and mutants for the ERG2 gene showed this protein present in a wide array of intracellular membranes, as well as at the plasma membrane, although they differed in their levels. On the whole, our data showed that endoplasmic reticulum/Golgi apparatus retention of the main glucan synthase subunit Fks1p, together with a lower polypeptide level, are probably some of the main mechanisms for cell wall weakness in ERG2 mutants . (AU)

• FAPESP's process: 16/07896-8 - Study of the mechanisms impairing cell wall maintenance by abnormal sterols in fungi
• Grantee: Leydi Roxana Gutiérrez Armijos
• Support Opportunities: Scholarships in Brazil - Master