Tao J, Ginsberg I, Banerjee N, Held W, Koltin Y, Bruenn J A
Department of Biological Sciences, State University of New York, Buffalo 14260.
Mol Cell Biol. 1990 Apr;10(4):1373-81. doi: 10.1128/mcb.10.4.1373-1381.1990.
There are a number of yeasts that secrete killer toxins, i.e., proteins lethal to sensitive cells of the same or related species. Ustilago maydis, a fungal pathogen of maize, also secretes killer toxins. The best characterized of the U. maydis killer toxins is the KP6 toxin, which consists of two small polypeptides that are not covalently linked. In this work, we show that both are encoded by one segment of the genome of a double-stranded RNA virus. They are synthesized as a preprotoxin that is processed in a manner very similar to that of the Saccharomyces cerevisiae k1 killer toxin, also encoded by a double-strand RNA virus. Active U. maydis KP6 toxin was secreted from S. cerevisiae transformants expressing the KP6 preprotoxin. The two secreted polypeptides were not glycosylated in U. maydis, but one was glycosylated in S. cerevisiae. Comparison of known and predicted cleavage sites among the five killer toxins of known sequence established a three-amino-acid specificity for a KEX2-like enzyme and predicted a new, undescribed processing enzyme in the secretory pathway in the fungi. The mature KP6 toxin polypeptides had hydrophobicity profiles similar to those of other known cellular toxins.
有许多酵母会分泌杀伤毒素，即对相同或相关物种的敏感细胞具有致死性的蛋白质。玉米的真菌病原体玉米黑粉菌也会分泌杀伤毒素。玉米黑粉菌杀伤毒素中研究得最清楚的是KP6毒素，它由两个非共价连接的小多肽组成。在这项研究中，我们表明这两个多肽均由双链RNA病毒基因组的一个片段编码。它们作为前原毒素合成，其加工方式与同样由双链RNA病毒编码的酿酒酵母k1杀伤毒素非常相似。活性玉米黑粉菌KP6毒素从表达KP6前原毒素的酿酒酵母转化体中分泌出来。这两个分泌的多肽在玉米黑粉菌中未被糖基化，但其中一个在酿酒酵母中被糖基化。对已知序列的五种杀伤毒素中已知和预测的切割位点进行比较，确定了一种类似KEX2酶的三个氨基酸特异性，并预测了真菌分泌途径中一种新的、未描述的加工酶。成熟的KP6毒素多肽的疏水性图谱与其他已知细胞毒素的相似。
