Final answer:
The N-end rule relates to how the N-terminal amino acid of a protein determines its stability and degradation. Destabilizing amino acids lead to rapid degradation, while stabilizing amino acids prevent it, allowing control over protein levels and function.
Step-by-step explanation:
The N-end Rule and Protein Stability
The N-end rule refers to a cellular process that dictates the lifespan and stability of a protein based on its N-terminal amino acid. This rule is critical for the targeted protein degradation, which is a fundamental aspect of cellular regulation and function. For the N-end rule to apply, certain destabilizing amino acids must be exposed at the N-terminus of the protein, leading to recognition and degradation by proteolytic systems. Conversely, stabilizing amino acids when present at the N-terminus, result in the protein being spared from rapid degradation.
The amino acid composition is highly conserved and biased towards certain amino acids at the N-terminus, such as stabilizing amino acids for regulated degradation. The result of this targeting is a refined control over protein levels and functions within the cell, which can be considered an early form of a 'punctuation system' for protein stability. Furthermore, protein termini statistics have shown a coherent overlap with the N-end rule, illustrating a cellular strategy to localize stabilizing amino acids at the protein's beginning and destabilizing ones at the end. This is crucial in understanding the proteolytic regulation of proteins.