Determining the Proteolytic Processing of K1-Like Killer Toxins by Kex1 and Kex2
Faculty Mentor Information
Dr. Paul Rowley, University of Idaho
Presentation Date
7-16-2026
Abstract
Killer toxins, antifungal proteins secreted by killer yeast, have the possibility to treat increasingly resistant fungal infections that account for 1.2 million deaths annually. The immature K1 killer toxin (pre-processed toxin), is comprised of four domains: delta, alpha, gamma, and beta. Cleavage at dibasic sites by Kex proteases is necessary for maturation of K1 prior to its secretion. K1 killer toxin-like (KKT) toxins are predicted to depend upon Kex proteases for maturation. Putative Kex cleavage sites have been identified for KKT toxins by sequence homology and molecular modeling, but it remains unknown if immature KKT toxins are processed in the same manner as K1. Western blot analysis shows C-terminally HA-tagged Kazachstania Africana KKT is processed and secreted while pre-processed toxin remains intracellular. Future experiments will use K. Africana KKT with two cleavage sites altered via site-directed mutagenesis to determine the locations of Kex cleavage. Mutant processing intermediates should be similar to processing intermediates found in Kex deletion strains, demonstrating protease-site specificity. Clarifying KKT processing will identify the maturation mechanism that is conserved over diverse toxins with minimal sequence homology.
Determining the Proteolytic Processing of K1-Like Killer Toxins by Kex1 and Kex2
Killer toxins, antifungal proteins secreted by killer yeast, have the possibility to treat increasingly resistant fungal infections that account for 1.2 million deaths annually. The immature K1 killer toxin (pre-processed toxin), is comprised of four domains: delta, alpha, gamma, and beta. Cleavage at dibasic sites by Kex proteases is necessary for maturation of K1 prior to its secretion. K1 killer toxin-like (KKT) toxins are predicted to depend upon Kex proteases for maturation. Putative Kex cleavage sites have been identified for KKT toxins by sequence homology and molecular modeling, but it remains unknown if immature KKT toxins are processed in the same manner as K1. Western blot analysis shows C-terminally HA-tagged Kazachstania Africana KKT is processed and secreted while pre-processed toxin remains intracellular. Future experiments will use K. Africana KKT with two cleavage sites altered via site-directed mutagenesis to determine the locations of Kex cleavage. Mutant processing intermediates should be similar to processing intermediates found in Kex deletion strains, demonstrating protease-site specificity. Clarifying KKT processing will identify the maturation mechanism that is conserved over diverse toxins with minimal sequence homology.