Tamás Markus J, Karlgren Sara, Bill Roslyn M, Hedfalk Kristina, Allegri Laura, Ferreira Marie, Thevelein Johan M, Rydström Jan, Mullins Jonathan G L, Hohmann Stefan
Department of Cell and Molecular Biology/Microbiology, Göteborg University, Box 462, 40530 Göteborg, Sweden.
J Biol Chem. 2003 Feb 21;278(8):6337-45. doi: 10.1074/jbc.M209792200. Epub 2002 Dec 16.
The controlled export of solutes is crucial for cellular adaptation to hypotonic conditions. In the yeast Saccharomyces cerevisiae glycerol export is mediated by Fps1p, a member of the major intrinsic protein (MIP) family of channel proteins. Here we describe a short regulatory domain that restricts glycerol transport through Fps1p. This domain is required for retention of cellular glycerol under hypertonic stress and hence acquisition of osmotolerance. It is located in the N-terminal cytoplasmic extension close to the first transmembrane domain. Several residues within that domain and its precise position are critical for channel control while the proximal residues 13-215 of the N-terminal extension are not required. The sequence of the regulatory domain and its position are perfectly conserved in orthologs from other yeast species. The regulatory domain has an amphiphilic character, and structural predictions indicate that it could fold back into the membrane bilayer. Remarkably, this domain has structural similarity to the channel forming loops B and E of Fps1p and other glycerol facilitators. Intragenic second-site suppressor mutations of the sensitivity to high osmolarity conferred by truncation of the regulatory domain caused diminished glycerol transport, confirming that elevated channel activity is the cause of the osmosensitive phenotype.
溶质的受控输出对于细胞适应低渗条件至关重要。在酿酒酵母中，甘油的输出由Fps1p介导，Fps1p是主要内在蛋白（MIP）家族通道蛋白的成员。在此，我们描述了一个短的调节结构域，它限制甘油通过Fps1p的运输。该结构域在高渗胁迫下对于细胞内甘油的保留以及因此获得渗透耐受性是必需的。它位于靠近第一个跨膜结构域的N端细胞质延伸部分。该结构域内的几个残基及其精确位置对于通道控制至关重要，而N端延伸部分的近端残基13 - 215则不是必需的。调节结构域的序列及其位置在其他酵母物种的直系同源物中完全保守。调节结构域具有两亲性，结构预测表明它可以回折到膜双层中。值得注意的是，该结构域与Fps1p和其他甘油转运体的通道形成环B和E具有结构相似性。由调节结构域截断导致的对高渗透压敏感性的基因内第二位点抑制突变导致甘油运输减少，证实通道活性升高是渗透敏感表型的原因。
