quaternary structure

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The structure formed by the noncovalent interaction of two or more macromolecules, such as that formed by four globin protein molecules to make hemoglobin or that formed by histones interacting with DNA to make a nucleosome.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun biochemistry, molecular biology The arrangement of multiple folded or coiled proteins to form a multi-subunit complex