Tertiærstruktur

Tertiærstruktur, or tertiary structure, is the overall three-dimensional arrangement of atoms in a single polypeptide chain. It describes how the polypeptide folds into a compact, functional shape that results from the spatial organization of its secondary elements—such as helices and sheets—and the surrounding side chains. The fold is stabilized by a combination of noncovalent interactions, including hydrogen bonds, ionic interactions, hydrophobic packing, and van der Waals forces, as well as covalent disulfide bonds in many proteins.

The folding process is driven by the primary sequence and influenced by the cellular environment. The sequence encodes the information necessary to achieve a low-energy conformation under physiological conditions, though folding can be affected by factors such as pH, temperature, ionic strength, and molecular chaperones. Some proteins may sample multiple conformations as part of their function or during folding.

Tertiary structure is closely linked to a protein’s function. The arrangement of active-site residues, binding pockets, and allosteric sites depends on the precise fold. Misfolding or instability of the tertiary structure can lead to loss of function and can contribute to diseases, including neurodegenerative disorders and some forms of amyloidoses. Cellular quality-control systems, such as chaperones and proteasomes, help maintain properly folded proteins.

Determination and study of tertiary structure employ techniques such as X-ray crystallography, nuclear magnetic resonance spectroscopy, and cryo-electron microscopy. Computational approaches, including homology modeling and advanced structure prediction methods like AlphaFold, complement experimental methods. Tertiary structure is distinct from quaternary structure, which describes the assembly of multiple polypeptide chains into a functional complex.