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.

中文翻译：

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C 末端氨基酸组成对细菌中蛋白质表达的影响。


蛋白质的 C 端序列涉及翻译终止效率和蛋白质降解等过程。然而，该 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，我们发现了细菌分类学（1,582 个基因组）中普遍存在的 C 端氨基酸偏差。我们发现带正电荷的氨基酸（赖氨酸、精氨酸）的频率较高，而疏水性氨基酸和苏氨酸的频率较低。然后，我们研究了肺炎支原体突变体文库中 C 末端组成对蛋白质水平的影响，涵盖了最后两个密码子的所有可能组合。我们发现带电和极性残基，特别是赖氨酸，导致较高的表达，而疏水性和芳香族残基导致较低的表达，蛋白质水平差异高达四倍。我们进一步表明，蛋白质降解率的调节可能是驱动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大影响。