3D DOMAIN SWAPPING - A MECHANISM FOR OLIGOMER ASSEMBLY

3D domain swapping is a mechanism for forming oligomeric proteins from their monomers. In 3D domain swapping, one domain of a monomeric prot ein is replaced by the same domain from an identical protein chain. Th e result is an intertwined dimer or higher oligomer, with one domain o f each subunit replaced by the identical domain from another subunit. The swapped ''domain'' can be as large as an entire tertiary globular domain, or as small as an a-helix or a strand of a P-sheet. Examples o f 3D domain swapping are reviewed that suggest domain swapping can ser ve as a mechanism for functional interconversion between monomers and oligomers, and that domain swapping may serve as a mechanism for evolu tion of some oligomeric proteins. Domain-swapped proteins present exam ples of a single protein chain folding into two distinct structures.