Editing Protein tertiary structure (section)

==== Thermostability ====
{{See also|Equilibrium unfolding}}
A protein folded into its [[native state]] or [[chemical conformation|native conformation]] typically has a lower [[Gibbs free energy]] (a combination of [[enthalpy]] and [[entropy]]) than the unfolded conformation. A protein will tend towards low-energy conformations, which will determine the protein's fold in the [[cell (biology)|cellular]] environment. Because many similar conformations will have similar energies, protein structures are [[Protein dynamics|dynamic]], fluctuating between these similar structures.

[[Globular protein]]s have a core of [[hydrophobic]] amino acid residues and a surface region of [[water]]-exposed, charged, [[hydrophilic]] residues. This arrangement may stabilize interactions within the tertiary structure. For example, in [[secrete]]d proteins, which are not bathed in [[cytoplasm]], [[disulfide bond]]s between [[cysteine]] residues help to maintain the tertiary structure. There is a commonality of stable tertiary structures seen in proteins of diverse function and diverse [[molecular evolution|evolution]]. For example, the [[TIM barrel]], named for the enzyme [[triosephosphateisomerase]], is a common tertiary structure as is the highly stable, [[dimer (chemistry)|dimeric]], [[coiled coil]] structure. Hence, proteins may be  classified by the structures they hold. Databases of proteins which use such a classification include ''[[Structural Classification of Proteins|SCOP]]'' and ''[[CATH]]''.