Protein quinary structure information

Protein quinary structure refers to the features of protein surfaces that are shaped by evolutionary adaptation to the physiological context of living cells.^[1][2][3][4] Quinary structure is thus the fifth level of protein complexity, additional to protein primary, secondary, tertiary and quaternary structures. As opposed to the first four levels of protein structure, which are relevant to isolated proteins in dilute conditions, quinary structure emerges from the crowdedness of the cellular context,^[5] in which transient encounters among macromolecules are constantly occurring.

In order to perform their functions, proteins often need to find a specific counterpart to which they will bind in a relatively long encounter. In a very crowded cytosol, in which proteins engage in a vast and complex network of attracting and repelling interactions, such search becomes challenging, because it involves sampling a huge space of possible partners, of which very few will be productive. A solution to this challenge requires that proteins spend as little time as possible on each encounter, so that they can explore a larger number of surfaces, while simultaneously making this interaction as intimate as possible, so if they do come across the right partner, they will not miss it.^[6] In this sense, quinary structure is the result of a series of adaptations present in protein surfaces, which allow proteins to navigate the complexity of the cellular environment.