The Protein Quartet model of protein function proposed by Uversky (Uversky V.
"Natively unfolded proteins: a point where biology waits for physics."
Protein Science, 2002, 11:739-56) specifies that function can arise from
any of the four conformations (Ordered, Molten Globule, Pre-Molten Globule,
Random Coil) or transitions between any two conformations. Accordingly
the following list of structural/functional types was adopted: