The roles of galactitol, galactose-1-phosphate, and phosphoglucomutase in galactose-induced toxicity in Saccharomyces cerevisiae
The roles of galactitol, galactose-1-phosphate, and phosphoglucomutase in galactose-induced toxicity in Saccharomyces cerevisiae
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DOI：
10.1002/bit.21890
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发表时间：
2008-10-01
影响因子：
3.8
通讯作者：
Nielsen, Jens
中科院分区：
文献类型：
--
作者：
de Jongh, Willem A.;Bro, Christoffer;Nielsen, Jens
酵母对半乳糖的吸收和分解代谢比葡萄糖和果糖低得多，在这种酵母利用含有半乳糖的复杂底物的应用中，例如，木质纤维素和棉子糖，这会导致发酵时间延长。半乳糖通过Leloir途径代谢，除了通过该途径提高通量具有工业意义外，研究Leloir途径也具有医学意义。因此，编码半乳糖-1-磷酸尿苷基转移酶或半乳糖激酶基因的遗传疾病导致半乳糖血症患者和酵母的半乳糖毒性。为了阐明半乳糖相关的毒性，这可能解释酿酒葡萄球菌的低摄取和分解代谢率，我们研究了半乳糖生长改善或受损的重组酿酒葡萄球菌菌株的生理特性和细胞内代谢物谱。GAL1、GAL2、GAL7和GAL10基因的编码蛋白共同将细胞外的半乳糖转化为葡萄糖-1-磷酸，不同组合过表达的菌株在半乳糖上的有氧批量培养显示，与参考菌株相比，最大特定生长速率降低。假设的有毒中间体半乳糖-1-磷酸不能是半乳糖相关毒性的唯一原因，但有迹象表明，半乳糖-1-磷酸可能通过抑制磷酸葡萄糖糖化酶而产生负面影响。此外，我们发现半乳糖醇在酿酒酵母中形成，并且细胞内半乳糖醇浓度升高以及半乳糖-1-磷酸浓度与磷酸葡萄糖糖化酶活性之间的比值似乎是导致半乳糖相关毒性降低的重要原因。
The uptake and catabolism of galactose by the yeast Saccharomyces cerevisiae is much lower than for glucose and fructose, and in applications of this yeast for utilization of complex substrates that contain galactose, for example, lignocellulose and raffinose, this causes prolonged fermentations. Galactose is metabolized via the Leloir pathway, and besides the industrial interest in improving the flux through this pathway it is also of medical relevance to study the Leloir pathway. Thus, genetic disorders in the genes encoding galactose-1-phosphate uridylyltransferase or galactokinase result in galactose toxicity both in patients with galactosemia and in yeast. In order to elucidate galactose related toxicity, which may explain the low uptake and catabolic rates of S. cerevisiae, we have studied the physiological characteristics and intracellular metabolite profiles of recombinant S. cerevisiae strains with improved or impaired growth on galactose. Aerobic batch cultivations on galactose of strains with different combinations of overexpression of the genes GAL1, GAL2, GAL7, and GAL10, which encode proteins that together convert extracellular galactose into glucose-1-phosphate, revealed a decrease in the maximum specific growth rate when compared to the reference strain. The hypothesized toxic intermediate galactose-1-phosphate cannot be the sole cause of galactose related toxicity, but indications were found that galactose-1-phosphate might cause a negative effect through inhibition of phosphoglucomutase. Furthermore, we show that galactitol is formed in S. cerevisiae, and that the combination of elevated intracellular galactitol concentration, and the ratio between galactose-1-phosphate concentration and phosphoglucomutase activity seems to be important for galactose related toxicity causing decreased growth rates.