Structural and functional analysis of the killer element pPin1-3 from Pichia inositovora

Area of Science:

• Microbiology
• Molecular Biology
• Yeast Genetics

Background:

• Killer yeasts produce toxins lethal to sensitive strains.
• Pichia inositovora harbors linear plasmids (pPin1-1, pPin1-3) conferring killer activity against Saccharomyces cerevisiae.
• The K. lactis killer toxin (zymocin) is well-characterized, providing a basis for comparison.

Purpose of the Study:

• To characterize the killer plasmid pPin1-3 from Pichia inositovora.
• To elucidate the molecular mechanisms and potential targets of the P. inositovora killer toxin.
• To compare the P. inositovora killer system with the known K. lactis zymocin system.

Main Methods:

• Cloning and sequencing of the pPin1-3 plasmid.
• Bioinformatic analysis of open reading frames (ORFs) and protein homology.
• Biochemical assays including chitin affinity chromatography and Western blot analysis.
• Gene disruption experiments in Saccharomyces cerevisiae (CHS3 and ELP3/TOT3).

Main Results:

• The pPin1-3 plasmid is 9683 bp with terminal inverted repeats and four ORFs.
• ORF3 encodes a protein with chitin-binding and chitinase domains, similar to zymocin's alpha-subunit.
• A secreted protein cross-reacts with anti-zymocin alpha-subunit antibodies.
• Disruption of CHS3 confers resistance, indicating chitin as the toxin receptor.
• Disruption of ELP3/TOT3 reduces sensitivity, suggesting a similar mode of action to zymocin.

Conclusions:

• Pichia inositovora killer plasmid pPin1-3 encodes a toxin with structural and functional similarities to K. lactis zymocin.
• Chitin is identified as the cellular receptor for the P. inositovora toxin.
• Despite genomic differences, the P. inositovora and K. lactis killer systems likely share similar mechanisms of action.