Folding, Modification and Degradation of Proteins
A proteins amino acid sequence, dictates its folding into a specific 3D conformation, the native state.Denatured protein folding, proceeds in vitro through intermediates having secondary and non-native tertiary structure.
In vivo, protein folding occurs with the assistance of two kinds of special proteins: Molecular chaperones (Hsp70 proteins) and Chaperonins (Hsp60- like proteins). Newly made polypeptides coming from ribosomes, bind to molecular chaperones which in turn prevent these new polypeptides to misfold. Chaperonins which are larger complexes than chaperone proteins, shelter partially folded or misfolded proteins in a barrel-like cavity which allows for additional time for proper folding.
After proteins are synthesized they are modified in many ways which in turn alter their structure and function.
Intracellular proteins life span is largely determined on their susceptibility to proteolytic degradation. The presence of certain internal sequences of N-terminal residues targets cytosolic proteins for addition of ubiquitin and subsequent proteolysis within a proteasome.