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KP4 fungal toxin inhibits growth in Ustilago maydis by blocking calcium uptake
M J Gage1, J Bruenn, M Fischer
1Donald Danforth Plant Science Center, 7425 Forsyth Boulevard, Box 1098, St Louis, MO 63105, USA.
Abstract:
KP4 is a virally encoded fungal toxin secreted by the P4 killer strain of Ustilago maydis. From our previous structural studies, it seemed unlikely that KP4 acts by forming channels in the target cell membrane. Instead, KP4 was proposed to act by blocking fungal calcium channels, as KP4 was shown to inhibit voltage-gated calcium channels in rat neuronal cells, and its effects on fungal cells were abrogated by exogenously added calcium. Here, we extend these studies and demonstrate that KP4 acts in a reversible manner on the cell membrane and does not kill the cells, but rather inhibits cell division. This action is mimicked by EGTA and is abrogated specifically by low concentrations of calcium or non-specifically by high ionic strength buffers. We also demonstrate that KP4 affects (45)Ca uptake in U. maydis. Finally, we show that cAMP and a cAMP analogue, N 6,2'-O-dibutyryladenosine 3':5'-cyclic monophosphate, both abrogate KP4 effects. These results suggest that KP4 may inhibit cell growth and division by blocking calcium-regulated signal transduction pathways.
Insights
The fungal toxin KP4 reversibly inhibits fungal cell division by blocking calcium channels and calcium-regulated signaling pathways, rather than killing cells. This effect is reversed by calcium or cAMP.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- KP4 is a fungal toxin from Ustilago maydis.
- Previous studies suggested KP4 inhibits calcium channels but did not clarify its mechanism.
- KP4's action on fungal cells was not fully understood.
Purpose of the Study:
- To elucidate the mechanism of action of the fungal toxin KP4.
- To investigate KP4's effect on fungal cell division and membrane interactions.
- To determine if KP4 interferes with calcium signaling pathways.
Main Methods:
- Investigated KP4's effect on Ustilago maydis cell division and membrane.
- Utilized EGTA, calcium concentrations, and ionic strength buffers to test KP4's action.
- Assessed (45)Ca uptake and the effects of cAMP and its analogue on KP4 activity.
Main Results:
- KP4 reversibly inhibits fungal cell division without causing cell death.
- KP4's effects are mimicked by EGTA and reversed by specific calcium concentrations or high ionic strength.
- KP4 affects (45)Ca uptake and its inhibitory effects are abrogated by cAMP.
Conclusions:
- KP4 likely inhibits fungal growth and division by blocking calcium-regulated signal transduction pathways.
- The toxin's action involves reversible membrane interaction and interference with calcium homeostasis.
- KP4 represents a potential tool for studying calcium signaling in fungi.