Yeast Killer Toxins: Fundamentals and Applications

Saccharomyces paradoxus K66 Killer System Evidences Expanded Assortment of Helper and Satellite Viruses

“…Thus, the maturation process of K66 toxin may proceed by two alternative scenarios: first, by removing pre-pro-sequence and potential γ-peptide (from 182 till 239 aa) and forming a disulfide-bonded α/β heterodimer. A similar structural organization is typical for almost all known S. cerevisiae killer toxins, except for the K2 killer protein lacking γ-subunit [ 15 , 62 ]. In the second scenario, the Kex2 protease may not cleave at the position 239 and, similar to the K2 killer protein, γ-peptide is not released.…”

“…Most killer toxins are encoded by dsRNA viruses called M satellites, which depend for their propagation and maintenance on an L-A helper virus [ 8 , 11 ]. Among the representatives of the genus Saccharomyces , the killer phenomenon has been studied most extensively in S. cerevisiae , where four different viral-originated killer toxins (K1, K2, K28, and Klus) have been described [ 12 , 13 , 14 , 15 ]. For effective functioning of the killer system, well organized communication between the functionally distinct ScV-LA and ScV-M viruses is required.…”

“…There are several variants of L-A (ScV-LA-1, ScV-LA-2, ScV-LA-28 and ScV-LA-lus), with an average of 74% identity in nucleotide sequences, associated with different M viruses and displaying distinct phenotypic properties [ 14 , 18 ]. Four different S. cerevisiae M dsRNA viruses have been described (ScV-M1, ScV-M2, ScV-M28 and ScV-Mlus) so far [ 15 ]. Certain relationships between L-A and M viruses have been observed (LA-1 and M1, LA-2 and M2, LA-lus and Mlus, LA-28 and M28) [ 14 , 18 , 19 ] and the possible role of the toxin-producing M viruses in selecting the L-A variants to support them has been proposed [ 19 ].…”

“…Different killer toxins are secreted glycoproteins lacking amino acid sequence conservation and adopting diverse cell killing mechanisms. The proposed mechanism of the action for the K1 and K2 toxins is a two-step process, whereby the killer protein first binds to the primary cell wall receptor-β-1,6-glucan [ 21 , 22 ], then, at the second step, the toxins approach a plasma membrane receptor and form lethal cation-selective ion channels [ 15 , 23 , 24 , 25 ]. In contrast, the K28 toxin binds to α-1,3-mannoproteins positioned in the cell wall, then interacts with a plasma membrane receptor Erd2 and enters the cell by endocytosis.…”

Modulating Wine Pleasantness Throughout Wine-Yeast Co-Inoculation or Sequential Inoculation

“…Co-inoculation involving S. cerevisiae and non-Saccharomyces yeasts species typically results in the disappearance (or the presence in relative low amounts) and loss of viability of non-Saccharomyces [65,66]. Though S. cerevisiae dominance can be explained by the depletion of sugar and nutrients from the grape must followed by ethanol production and lack of oxygen, some direct mechanisms for yeast species antagonism have also been described: (i) killer factors (so-called killer toxins or killer proteins), which are secreted peptides, encoded by extrachromosomal elements of S. cerevisiae that affect other yeast species [67]; (ii) similar compounds have also been described for Torulaspora delbrueckii species [68] and for the genera Pichia, Kluyveromyces, Lachancea, Candida, Cryptococcus, Debaryomyces, Hanseniaspora, Hansenula, Kluyveromyces, Metschnikowia, Torulopsis, Ustilago, Williopsis, and Zygosaccharomyces, indicating that the killer phenomenon is indeed widespread among yeasts. [69]; (iii) S. cerevisiae are also able to secret antimicrobial peptides (AMPs) during alcoholic fermentation that are active against wine-related yeasts (e.g., Dekkera bruxellensis) and bacteria (e.g., Oenococcus oeni).…”