Embracing proteins: structural themes in aptamer-protein complexes

Understanding the structural rules that govern specific, high affinity binding characteristic of aptamer-protein interactions is important in view of the increasing use of aptamers across many applications. From the modest number of 16 aptamer protein structures currently available, trends are emerging. The flexible phosphodiester backbone allows folding into precise threedimensional structures using known nucleic acid motifs as scaffolds that orient specific functional groups for target recognition. Still, completely novel motifs essential for structure and function are found in modified aptamers with diversity enhancing side chains. Aptamers and antibodies, two classes of macromolecules used as affinity reagents with entirely different backbones and composition, recognize protein epitopes of similar size and with comparably high shape complementarity.