/ˈkwɒt ərˌnɛr I ˈstrʌk tʃər/

noun

In proteins, the number and arrangement of folded protein subunits (polypeptides) in the final protein molecule (multi subunit complex). In nucleic acids, quaternary structure can refer to the high level organization of DNA in chromatin including its interactions with histones.

Latin, from quaternārius & structūra