logo.gif (3296 bytes)Introduction to Protein Structure

Quartenary Structure

Multisubunit proteins consist of more than one polypeptide chain. Each subunit (polypetide) folds more-or-less independently, as do "regular" proteins. The subunits then associate, generally via noncovalent interactions (although some proteins do have intersubunit disulfide bonds), to form the final structure. This is refered to as quartenary structure.

Hemoglobin is one example of a multisubunit protein. Hemoglobin has an a2b2 structure. It consists of four polypepitides, two alpha subunits and two beta subunits. Each subunit also contains a nonprotein group called heme that is essential for hemoglobin's function (i.e. oxygen transport).


     heme groups: 
    Color by:


         (helix; sheet; other)





Copyright 1998, 1999, 2007 by Frank R. Gorga;   Page maintained by F.R. Gorga;   Last updated: 12-Mar-2007