Nanoparticle Self-Assembly Directed by Antagonistic Kinase and Phosphatase Activities

Reversible self-assembly is ubiquitous in Nature. The ability to dynamically control the assembly and disassembly of biomolecular complexes is essential to higher-order biological processes, including the control of intracellular communication, gene expression, and platelet aggregation upon injury. To date, assembly or disassembly of nanoparticles (NPs) has been exploited to improve sensitivity for detection of single biomolecular targets, including DNA, small molecules, proteins, and pH changes in vitro; however, mechanisms of sensing that allow multiple, opposing stimuli to dynamically assemble and dis-assemble NPs have not been described. Development of inorganic nanoparticles that respond to multiple, antagonistic biological signals could facilitate sensing of the physiologic balance between opposing effectors of cellular and tissue function. Herein, we introduce a nanoparticle (NP) system where self-assembly is dynamically coupled to the balance between the classic antagonistic enzymes: tyrosine kinase and phosphatase. In vivo, these enzymes regulate cellular communication, gene expression, and ultimately cell life and death through the phosphorylation and dephosphorylation of tyrosine residues on other proteins Their dysregulation contributes significantly to the development of cancer and other inflammatory diseases. Here, kinase-induced superparamagnetic nanoassemblies enhance the T2 relaxation of hydrogen atoms at picomolar enzyme concentrations and are shown to be fully reversible by introducing excess phosphatase activity. In the future, these nanomaterials may be optimized to report the balance between these cytosolic enzyme activities and may facilitate new screens for inhibitors in vitro and in vivo. Additionally, extensions of this design logic may be synthesized to probe the dynamics of a diversity of antagonistic biologic processes. To construct a system of NPs that could coalesce in the presence of kinase activity and re-disperse in the presence of phosphatase activity, two NP populations were synthesized (Scheme 1). The first population was modified with peptide substrates that may be phosphorylated by Abl tyrosine kinase and dephosphorylated by a phosphatase. The second popula-