細菌のタンパク質成熟

The N-terminus undergoes cotranslational modifications as the polypeptide exits the ribosome. The N-formyl group is enzymatically removed from N-formylmethionine, the first amino acid. In some cases, one or more N-terminal amino acids are excised. These early modifications are crucial for downstream protein functionality and stability.

ATP-independent chaperones like trigger factor bind the ribosome and interact with emerging polypeptides, preventing premature folding or aggregation without energy consumption. ATP-dependent chaperones such as DnaK and DnaJ use ATP hydrolysis to prevent improper polypeptide folding and stabilize unfolded regions in larger proteins, offering more active intervention in the folding process.

The GroEL-GroES complex receives partially folded large proteins from the DnaK/DnaJ system. It forms a barrel-shaped structure that encapsulates misfolded proteins in a protected cytoplasmic environment, providing isolation for refolding. This compartmentalization allows proteins to refold correctly without interference from the cellular environment.

Heat shock proteins like Hsp70 refold proteins that become denatured during high-temperature conditions, restoring their functionality for reuse. When proteins are irreparably damaged by heat stress, Hsp70 directs them toward degradation pathways, preserving cellular integrity and preventing accumulation of non-functional proteins.

Cold shock proteins such as CspA function as RNA chaperones that stabilize mRNA at low temperatures. They prevent secondary structure formation in mRNA, ensuring efficient translation of proteins necessary for bacterial survival during cold stress. This stabilization maintains protein synthesis capacity when environmental temperatures drop.

Chaperone proteins prevent polypeptide aggregation and facilitate correct functional folding, which is critical for protein activity. They work throughout maturation, from nascent polypeptide emergence at the ribosome through post-translational modifications. This assistance ensures proteins achieve proper conformations necessary for cellular function and adaptation to environmental changes.

Bacterial protein maturation is the final step in gene expression, ensuring newly synthesized polypeptides achieve correct functional conformations through coordinated modifications and quality control. This process integrates with coordination of gene expression processes in bacteria, where transcription, translation, and post-translational modifications work together to produce functional proteins.