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From genes to proteins: How to regulate the protein synthesis process through ribosomes?
In the world of cell biology, protein synthesis starts from genes and undergoes a complex regulatory process to finally form functional proteins. In this process, ribosomes play an indispensable role as the center of translation, responsible for converting messenger RNA into polypeptide chains. Beyond simple protein synthesis, regulation of this process is critical to maintaining intracellular protein homeostasis (proteostasis).
Protein synthesis within cells not only involves the transmission of genetic information, but also requires precise folding to avoid errors and aggregation, which is the cornerstone of cellular health.
The protein synthesis process begins with specialized sequences encoded by a gene's DNA, followed by a transcription step to produce messenger RNA (mRNA). Next, the mRNA is transported to the ribosome, where several important factors work together to ensure the precise manufacture of the protein. Ribosomes help bind together corresponding chains of amino acids to form polypeptide chains, the rudiments of proteins.
Regulation of ribosomes and protein synthesis
During the protein synthesis process, the ribosome is not only a "factory", its structural characteristics also affect protein folding and future interactions. When the ribosome encounters a rare codon, the rate of synthesis may slow, giving each protein domain the time it needs to fold correctly.
For example, the exit channel of the ribosome (width range: 10Å to 20Å, length 80Å) controls the preliminary structure of the newly synthesized polypeptide chain, avoiding the problem of premature folding.
The new polypeptide chain enters the intracellular environment through the narrow exit of the ribosome. During this process, the properties of the ribosome promote the formation of certain secondary structures, such as α-helices, while limiting excessive interactions of the polypeptide chain. In this way, good conditions can be provided for the correct folding of multi-domain proteins.
Molecular chaperones and post-translational maintenance
After protein synthesis, cells use molecular chaperones to maintain protein homeostasis. These chaperone proteins recognize exposed hydrophobic amino acid segments in newly synthesized polypeptide chains and promote their correct formation.
Chaperone proteins such as trigger factors can stabilize polypeptides, promote their folding, and prevent protein aggregation.
The work of chaperone proteins begins when the polypeptide chain is longer than 60 amino acids. This process ensures correct folding of the polypeptide chain, helping to avoid subsequent problems caused by aggregation and failed folding.
Regulation of protein degradation
Promoting protein degradation is another important component of the proteostasis network. The protein degradation process is initiated when signals within the cell indicate the need to reduce overall cellular protein levels. This process directly affects not only the specific proteins lost, but also the entire protein mix.
For example, when unfolded or misfolded proteins are found, they are often degraded, a process called the unfolded protein response (UPR) or endoplasmic reticulum-associated protein degradation (ERAD).
Cells can also degrade proteins through mechanisms such as autophagy. These processes are critical for maintaining intracellular protein homeostasis and are closely related to cell health.
Signaling events and cellular responses
Cellular responses to protein misfolding involve specific detection mechanisms. These mechanisms, whether in the cytoplasm, endoplasmic reticulum or mitochondria, can detect abnormal proteins and initiate corresponding protective mechanisms.
For example, the cellular heat shock response (HSR) can be regulated by heat shock transcription factors (HSFs), which initiate gene expression to enhance protein homeostasis when stimulated by protein misfolding.
These responses are not only a mechanism of cell self-defense, but can also be extended to other tissues through the intercellular communication system to form a systemic protective response.
Relationship between disease and protein homeostasis
Disorders of protein homeostasis are closely related to a variety of diseases, such as cystic fibrosis, Huntington's disease, and Alzheimer's disease. These diseases are often caused by errors or mutations in the protein folding process, leading to its aggregation or loss of function.
Therefore, understanding the processes of protein synthesis and degradation is of great significance for the treatment of these diseases.
With in-depth research on the regulatory mechanisms of protein homeostasis, there will be opportunities in the future to repair these dysfunctions through drug intervention and ultimately improve the health of patients. This makes people think, how to promote the restoration of protein homeostasis and the treatment of diseases in a more effective way?
