Altered Binding of a Multimeric Protein by Changing the Self-Assembling Properties of its Substrate

Artificially controlled cell recognition has potentially far-reaching applications in both the understanding and altering of biological function. The event of recognition often involves a multimeric protein binding a cellular membrane. While such an interaction is energetically favorable, it has been surprisingly underexploited in artificial control of recognition. Herein we describe how changing properties of substrate (phosphocholine, PC) self-assembly can affect both binding behavior and substrate affinity to a pentameric recognition protein (C-reactive protein, CRP). PC was modified with a short, self-assembling DNA strand to make the substrate self-assembly sensitive and responsive to ionic environment. A significant shift in CRP binding affinity was observed when substrates were assembled in the presence of Cs+ rather than K. Furthermore, alteration of the linker length tethering PC to DNA showed trends similar to other multivalent systems. In optimizing these linker lengths, positive cooperativity increased and K-d of the substrate assembly to CRP improved roughly 1000-fold. Such experiments both inform our understanding of biological, multivalent interactions in self-assembling systems and present a potential method to exogenously control events in cell recognition.