Mattanovich Diethard, Gasser Brigitte, Hohenblum Hubertus, Sauer Michael
Institute of Applied Microbiology, BOKU--University of Natural Resources and Applied Life Sciences, Muthgasse 18, A-1190 Vienna, Austria.
J Biotechnol. 2004 Sep 30;113(1-3):121-35. doi: 10.1016/j.jbiotec.2004.04.035.
It is well established today that heterologous overexpression of proteins is connected with different stress reactions. The expression of a foreign protein at a high level may either directly limit other cellular processes by competing for their substrates, or indirectly interfere with metabolism, if their manufacture is blocked, thus inducing a stress reaction of the cell. Especially the unfolded protein response (UPR) in Saccharomyces cerevisiae (as well as some other yeasts) is well documented, and its role for the limitation of expression levels is discussed. One potential consequence of endoplasmatic reticulum folding limitations is the ER associated protein degradation (ERAD) involving retrotranslocation and decay in the cytosol. High cell density fermentation, the typical process design for recombinant yeasts, exerts growth conditions that deviate far from the natural environment of the cells. Thus, different environmental stresses may be exerted on the host. High osmolarity, low pH and low temperature are typical stress factors. Whereas the molecular pathways of stress responses are well characterized, there is a lack of knowledge concerning the impact of stress responses on industrial production processes. Accordingly, most metabolic engineering approaches conducted so far target at the improvement of protein folding and secretion, whereas only few examples of cell engineering against general stress sensitivity were published. Apart from discussing well-documented stress reactions of yeasts in the context of heterologous protein production, some more speculative topics like quorum sensing and apoptosis are addressed.
如今已充分证实，蛋白质的异源过表达与不同的应激反应相关。高水平表达外源蛋白可能会通过竞争底物直接限制其他细胞过程，或者在其合成受阻时间接干扰代谢，从而引发细胞的应激反应。特别是酿酒酵母（以及其他一些酵母）中的未折叠蛋白反应（UPR）已有充分记录，并且其在限制表达水平方面的作用也已得到讨论。内质网折叠限制的一个潜在后果是内质网相关蛋白降解（ERAD），它涉及逆转位和在细胞质中的降解。高细胞密度发酵是重组酵母的典型工艺设计，其施加的生长条件与细胞的自然环境相差甚远。因此，宿主可能会受到不同的环境压力。高渗透压、低pH值和低温是典型的应激因素。虽然应激反应的分子途径已得到充分表征，但关于应激反应对工业生产过程的影响仍缺乏了解。因此，迄今为止进行的大多数代谢工程方法都旨在改善蛋白质折叠和分泌，而针对一般应激敏感性的细胞工程实例则很少发表。除了在异源蛋白生产的背景下讨论酵母中已充分记录的应激反应外，还涉及一些更具推测性的主题，如群体感应和细胞凋亡。
