Department of Chemistry, Faculty of Science and Technology, University of Tromsø, Tromsø, Norway.
PLoS One. 2012;7(12):e51761. doi: 10.1371/journal.pone.0051761. Epub 2012 Dec 17.
Cold-adaptation strategies have been studied in multiple psychrophilic organisms, especially for psychrophilic enzymes. Decreased enzyme activity caused by low temperatures as well as a higher viscosity of the aqueous environment require certain adaptations to the metabolic machinery of the cell. In addition to this, low temperature has deleterious effects on the lipid bilayer of bacterial membranes and therefore might also affect the embedded membrane proteins. Little is known about the adaptation of membrane proteins to stresses of the cold. In this study we investigate a set of 66 membrane proteins from the core genome of the bacterial family Vibrionaceae to identify general characteristics that discern psychrophilic and mesophilic membrane proteins. Bioinformatical and statistical methods were used to analyze the alignments of the three temperature groups mesophilic, intermediate and psychrophilic. Surprisingly, our results show little or no adaptation to low temperature for those parts of the proteins that are predicted to be inside the membrane. However, changes in amino acid composition and hydrophobicity are found for complete sequences and sequence parts outside the lipid bilayer. Among others, the results presented here indicate a preference for helix-breaking and destabilizing amino acids Ile, Asp and Thr and an avoidance of the helix-forming amino acid Ala in the amino acid composition of psychrophilic membrane proteins. Furthermore, we identified a lower overall hydrophobicity of psychrophilic membrane proteins in comparison to their mesophilic homologs. These results support the stability-flexibility hypothesis and link the cold-adaptation strategies of membrane proteins to those of loop regions of psychrophilic enzymes.
人们已经在多种嗜冷生物中研究了冷适应策略,尤其是针对嗜冷酶。低温导致的酶活性降低以及水相环境的较高黏度需要对细胞的代谢机制进行某些适应。除此之外,低温对细菌膜的脂双层有有害影响,因此也可能影响嵌入膜蛋白。对于膜蛋白对低温胁迫的适应,人们知之甚少。在这项研究中,我们研究了一组来自细菌科弧菌科核心基因组的 66 种膜蛋白,以确定区分嗜冷和中温膜蛋白的一般特征。我们使用生物信息学和统计方法分析了中温、中间温度和嗜冷这三组膜蛋白的比对结果。令人惊讶的是,我们的结果表明,对于那些预测位于膜内的蛋白质部分,几乎没有或没有对低温的适应。然而,在完整序列和位于脂质双层之外的序列部分中发现了氨基酸组成和疏水性的变化。其中,这里呈现的结果表明,在嗜冷膜蛋白的氨基酸组成中,存在偏好打破螺旋和使螺旋不稳定的氨基酸 Ile、Asp 和 Thr,以及避免形成螺旋的氨基酸 Ala。此外,与中温同系物相比,我们发现嗜冷膜蛋白的整体疏水性较低。这些结果支持稳定性-柔韧性假说,并将膜蛋白的冷适应策略与嗜冷酶的环区适应策略联系起来。