Musinova Yana R, Kananykhina Eugenia Y, Potashnikova Daria M, Lisitsyna Olga M, Sheval Eugene V
Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119991, Russia.
Department of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow 119991, Russia.
Biochim Biophys Acta. 2015 Jan;1853(1):101-10. doi: 10.1016/j.bbamcr.2014.10.007. Epub 2014 Oct 12.
The majority of known nucleolar proteins are freely exchanged between the nucleolus and the surrounding nucleoplasm. One way proteins are retained in the nucleoli is by the presence of specific amino acid sequences, namely nucleolar localization signals (NoLSs). The mechanism by which NoLSs retain proteins inside the nucleoli is still unclear. Here, we present data showing that the charge-dependent (electrostatic) interactions of NoLSs with nucleolar components lead to nucleolar accumulation as follows: (i) known NoLSs are enriched in positively charged amino acids, but the NoLS structure is highly heterogeneous, and it is not possible to identify a consensus sequence for this type of signal; (ii) in two analyzed proteins (NF-κB-inducing kinase and HIV-1 Tat), the NoLS corresponds to a region that is enriched for positively charged amino acid residues; substituting charged amino acids with non-charged ones reduced the nucleolar accumulation in proportion to the charge reduction, and nucleolar accumulation efficiency was strongly correlated with the predicted charge of the tested sequences; and (iii) sequences containing only lysine or arginine residues (which were referred to as imitative NoLSs, or iNoLSs) are accumulated in the nucleoli in a charge-dependent manner. The results of experiments with iNoLSs suggested that charge-dependent accumulation inside the nucleoli was dependent on interactions with nucleolar RNAs. The results of this work are consistent with the hypothesis that nucleolar protein accumulation by NoLSs can be determined by the electrostatic interaction of positively charged regions with nucleolar RNAs rather than by any sequence-specific mechanism.
大多数已知的核仁蛋白在核仁与周围核质之间自由交换。蛋白质保留在核仁中的一种方式是通过特定氨基酸序列的存在，即核仁定位信号（NoLSs）。NoLSs将蛋白质保留在核仁内部的机制仍不清楚。在这里，我们提供的数据表明，NoLSs与核仁成分之间的电荷依赖性（静电）相互作用导致核仁积累，具体如下：（i）已知的NoLSs富含带正电荷的氨基酸，但NoLS结构高度异质，无法确定这类信号的共有序列；（ii）在两种分析的蛋白质（NF-κB诱导激酶和HIV-1 Tat）中，NoLS对应于富含带正电荷氨基酸残基的区域；用不带电荷的氨基酸取代带电荷的氨基酸，核仁积累会随着电荷减少而成比例降低，并且核仁积累效率与测试序列的预测电荷密切相关；（iii）仅包含赖氨酸或精氨酸残基的序列（称为模拟NoLSs，或iNoLSs）以电荷依赖性方式在核仁中积累。iNoLSs的实验结果表明，核仁内的电荷依赖性积累取决于与核仁RNA的相互作用。这项工作的结果与以下假设一致，即NoLSs导致的核仁蛋白积累可由带正电区域与核仁RNA的静电相互作用决定，而非由任何序列特异性机制决定。
