Tuesday, March 1, 2011
A Protein Folding Experiment Shows Secondary Structure Does Not Form Before Tertiary Structure
This high-level summary gives an idea of the immense complexity of proteins, but there are a great many more details. For instance, protein molecular structures fall into a four-level hierarchy. The line of amino acids attached one to the next is called the protein’s primary structure. This line forms repeating patterns (helices and strands) in the folded up protein called the protein’s secondary structure. The folded up protein is called the tertiary structure. And proteins binding together form the quaternary structure.
But these structures may not always appear in this order. For instance, the secondary structure may form as a consequence of the tertiary structure coming together, rather than forming before this folding up process. Also, the tertiary structure may not form until the protein binds with its partner to form the quaternary structure.
These two facts were used in new research. A peptide that forms its tertiary structure after binding with its partner was used to determine when the peptide's secondary structure forms. Such secondary structure might provide a good framework as the peptide binds to the protein. But the researchers found that the secondary structure is not present as the peptide is folding. Rather, it appears after binding with the partner protein, and after the folding process.