Editing Protein tertiary structure (section)

==== Kinetic traps ====
Folding [[Chemical kinetics|kinetics]] may trap a protein in a high-[[energy]] conformation, i.e. a high-energy intermediate conformation blocks access to the lowest-energy conformation. The high-energy conformation may contribute to the function of the protein. For example, the [[influenza]] [[hemagglutinin]] protein is a single polypeptide chain which when activated, is [[proteolysis|proteolytically]] cleaved to form two polypeptide chains. The two chains are held in a high-energy conformation. When the local [[pH]] drops, the protein undergoes an energetically favorable conformational rearrangement that enables it to penetrate the host [[cell membrane]].