Weierstall T, Hollenberg C P, Boles E
Institut für Mikrobiologie, Heinrich-Heine-Universität, Düsseldorf, Germany.
Mol Microbiol. 1999 Feb;31(3):871-83. doi: 10.1046/j.1365-2958.1999.01224.x.
We have identified and characterized three genes, SUT1, SUT2 and SUT3, that encode glucose transporters of the yeast Pichia stipitis. When expressed in a Saccharomyces cerevisiae hxt null mutant strain that is unable to take up monosaccharides, all three proteins restored growth on glucose. Sequencing of the genes revealed open reading frames coding for 553 amino acids in the case of SUT1, and for 550 amino acids in the case of SUT2 and of SUT3. The derived protein sequences are closely related to one another, and show distinct sequence similarities to the S. cerevisiae hexose transporter family and to monosaccharide transporters of other organisms. The Sut2 and Sut3 proteins are nearly identical and differ only in one amino acid. Determination of substrate specificities and kinetic parameters of the individual Sut proteins expressed in a S. cerevisiae hxt1-7 mutant revealed Sut1, Sut2 and Sut3 as glucose transporters with K(m) values in the millimolar range. The proteins were also able to transport xylose and other monosaccharides, but with a considerably lower affinity. In P. stipitis, transcription of SUT1 was strongly induced by glucose and was independent of the oxygen supply. In contrast, SUT2 and SUT3 were only expressed under aerobic conditions, but independent of the carbon source. Cells disrupted for the SUT1 gene did not show any obvious growth phenotype, however low-affinity glucose uptake was lost. Further investigations suggest that the Sut proteins constitute a subfamily of glucose transporters in P. stipitis, and that other and probably unrelated proteins exist additionally mediating high-affinity glucose and xylose uptake.
我们已经鉴定并表征了三个基因，即SUT1、SUT2和SUT3，它们编码树干毕赤酵母的葡萄糖转运蛋白。当在无法摄取单糖的酿酒酵母hxt缺失突变株中表达时，这三种蛋白质都恢复了在葡萄糖上的生长。基因测序显示，SUT1编码一个由553个氨基酸组成的开放阅读框，SUT2和SUT3编码一个由550个氨基酸组成的开放阅读框。推导的蛋白质序列彼此密切相关，并且与酿酒酵母己糖转运蛋白家族以及其他生物体的单糖转运蛋白具有明显的序列相似性。Sut2和Sut3蛋白几乎相同，仅在一个氨基酸上有所不同。对在酿酒酵母hxt1-7突变体中表达的各个Sut蛋白的底物特异性和动力学参数的测定表明，Sut1、Sut2和Sut3是葡萄糖转运蛋白，其K(m)值在毫摩尔范围内。这些蛋白质也能够转运木糖和其他单糖，但亲和力要低得多。在树干毕赤酵母中，SUT1的转录受到葡萄糖的强烈诱导，并且与氧气供应无关。相比之下，SUT2和SUT3仅在有氧条件下表达，但与碳源无关。SUT1基因被破坏的细胞没有显示出任何明显的生长表型，然而低亲和力的葡萄糖摄取丧失了。进一步的研究表明，Sut蛋白构成了树干毕赤酵母中葡萄糖转运蛋白的一个亚家族，并且可能还存在其他不相关的蛋白介导高亲和力的葡萄糖和木糖摄取。
