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Identification and characterization of Schizophyllum commune type I metacaspases
Lakhena Leang1, Molly C McDonald1, Charlotte R Mineo1
1Department of Chemistry, Union College, Schenectady, NY, 12308, USA.
Abstract:
The role of programmed cell death in filamentous fungi is not well-understood, but is important due to the role of fungi in opportunistic infections. Plants, fungi and protozoa do not have caspase genes, but instead express the homologous proteins denoted metacaspases. To better understand the role of metacaspases in fungi we present an analysis of the sequences and activities of all five Type I metacaspases from Schizophyllum commune (ScMC), a mushroom-forming basiodmycete that undergoes sexual reproduction. The five Type I metacaspases of S. commune can be divided into two groups based on sequence similarity. Enzymes both with and without the N-terminal prodomain are active, but here we report on the constructs without the prodomains (Δpro). All five ScMCΔpro proteins show the highest enzymatic activity between pH 7 and 8 and require calcium for optimal activity. Optimal Ca2+ concentrations for ScMC1Δpro and ScMC2Δpro are 50 mM, while ScMC3, ScMC4Δpro and ScMC5Δpro activity is optimal around 5 mM calcium. All five S. commune metacaspases have similar substrate specificity. They are most active with Arg in the P1 position and inactive with Asp in the P1 position.
Insights
Programmed cell death in fungi is poorly understood. This study analyzes five metacaspases from *Schizophyllum commune*, revealing their calcium-dependent activity and substrate specificity, crucial for understanding fungal biology.
Area of Science:
- Mycology
- Molecular Biology
- Biochemistry
Background:
- Programmed cell death (PCD) in filamentous fungi is not well-understood, yet fungi play significant roles in opportunistic infections.
- Unlike animals, plants, fungi, and protozoa lack caspase genes and instead utilize homologous metacaspase proteins.
Purpose of the Study:
- To investigate the role of metacaspases in fungi by analyzing the sequences and activities of all five Type I metacaspases from *Schizophyllum commune* (ScMC).
Main Methods:
- Sequence analysis of five Type I metacaspases from *Schizophyllum commune*.
- Enzymatic activity assays of metacaspase constructs lacking N-terminal prodomains (Δpro) under varying pH and calcium concentrations.
- Determination of substrate specificity for the five ScMCΔpro proteins.
Main Results:
- The five *Sc*MC proteins were divided into two groups based on sequence similarity.
- All five *Sc*MCΔpro proteins exhibited optimal enzymatic activity between pH 7 and 8, requiring calcium.
- Optimal calcium concentrations varied, with *Sc*MC1Δpro and *Sc*MC2Δpro requiring 50 mM, while *Sc*MC3, *Sc*MC4Δpro, and *Sc*MC5Δpro were optimal around 5 mM.
- All five metacaspases demonstrated similar substrate specificity, being most active with Arg in the P1 position and inactive with Asp in the P1 position.
Conclusions:
- The study characterizes the biochemical properties of *Schizophyllum commune* metacaspases, providing insights into their function in fungal programmed cell death.
- Metacaspase activity is dependent on pH and calcium concentration, with specific preferences observed for different ScMC proteins.
- Identified substrate specificity suggests a role in cleaving proteins at Arginine residues, contributing to the understanding of fungal PCD mechanisms.
