Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Barcelona, Spain.
Universitat Pompeu Fabra (UPF), Barcelona, Spain.
Mol Syst Biol. 2020 May;16(5):e9208. doi: 10.15252/msb.20199208.
The C-terminal sequence of a protein is involved in processes such as efficiency of translation termination and protein degradation. However, the general relationship between features of this C-terminal sequence and levels of protein expression remains unknown. Here, we identified C-terminal amino acid biases that are ubiquitous across the bacterial taxonomy (1,582 genomes). We showed that the frequency is higher for positively charged amino acids (lysine, arginine), while hydrophobic amino acids and threonine are lower. We then studied the impact of C-terminal composition on protein levels in a library of Mycoplasma pneumoniae mutants, covering all possible combinations of the two last codons. We found that charged and polar residues, in particular lysine, led to higher expression, while hydrophobic and aromatic residues led to lower expression, with a difference in protein levels up to fourfold. We further showed that modulation of protein degradation rate could be one of the main mechanisms driving these differences. Our results demonstrate that the identity of the last amino acids has a strong influence on protein expression levels.
蛋白质的 C 末端序列参与了翻译终止效率和蛋白质降解等过程。然而，这个 C 末端序列的特征与蛋白质表达水平之间的一般关系仍然未知。在这里，我们鉴定了细菌分类学（1582 个基因组）中普遍存在的 C 末端氨基酸偏好性。我们表明，带正电荷的氨基酸（赖氨酸、精氨酸）的频率更高，而疏水性氨基酸和苏氨酸的频率更低。然后，我们在覆盖了最后两个密码子所有可能组合的肺炎支原体突变体文库中研究了 C 末端组成对蛋白质水平的影响。我们发现，带电荷和极性的残基，特别是赖氨酸，导致更高的表达，而疏水性和芳香族残基导致更低的表达，蛋白质水平的差异高达四倍。我们进一步表明，蛋白质降解率的调节可能是导致这些差异的主要机制之一。我们的结果表明，最后一个氨基酸的身份对蛋白质表达水平有很强的影响。
