1kve
From Proteopedia
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KILLER TOXIN FROM HALOTOLERANT YEAST
Overview
BACKGROUND: Several strains of yeasts and fungi produce proteinous, substances, termed killer toxins, which kill sensitive strains. The SMK, toxin, secreted by the halotolerant yeast Pichia farinosa KK1 strain, uniquely exhibits its maximum killer activity under conditions of acidic, pH and high salt concentration. The toxin is composed of two distinct, subunits, alpha and beta, which tightly interact with each other under, acidic conditions. However, they are easily dissociated under neutral, conditions and lose the killer activity. The three-dimensional structure, of the SMK toxin will provide a better understanding of the mechanism of, toxicity of this protein and the cause of its unique pH-dependent, stability. RESULTS: Two crystal structures of the SMK toxin have been, determined at 1.8 A resolution in different ionic strength conditions. The, two subunits, alpha and beta, are jointly folded into an ellipsoidal, single domain structure belonging to the alpha/beta-sandwich family. The, folding topology of the SMK toxin is essentially the same as that of the, fungal killer toxin, KP4. This shared topology contains two left-handed, split betaalphabeta motifs, which are rare in the other proteins. Many, acidic residues are clustered at the bottom of the SMK toxin molecule., Some of the carboxyl sidechains interact with each other through hydrogen, bonds. The ionic strength difference induces no evident structural change, of the SMK toxin except that, in the high ionic strength crystal, a number, of sulfate ions are electrostatically bound near the basic residues which, are also locally distributed at the bottom of the toxin molecule., CONCLUSIONS: The two killer toxins, SMK and KP4, share a unique folding, topology which contains a rare structural motif. This observation may, suggest that these toxins are evolutionally and/or functionally related., The pH-dependent stability of the SMK toxin is a result of the intensive, interactions between the carboxyl groups. This finding is important for, protein engineering, for instance, towards stabilization of the toxin, molecule in a broader pH range. The present crystallographic study, revealed that the structure of the SMK toxin itself is hardly affected by, the ionic strength, implying that a high salt concentration affects the, sensitivity of the cell against the toxin.
About this Structure
1KVE is a Protein complex structure of sequences from Pichia farinosa. Full crystallographic information is available from OCA.
Reference
The novel acidophilic structure of the killer toxin from halotolerant yeast demonstrates remarkable folding similarity with a fungal killer toxin., Kashiwagi T, Kunishima N, Suzuki C, Tsuchiya F, Nikkuni S, Arata Y, Morikawa K, Structure. 1997 Jan 15;5(1):81-94. PMID:9016714
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