Fig. 1
Design of smart copolymer. a Abundant phosphorylation sites located near the tubulin-binding domain of a microtubule-associated protein—Tau; the abnormal hyperphosphorylation of Tau is closely associated with several neurodegenerative disorders. Panel a is drawn based on the site information collected in PhosphoSitePlus database. b Chemical structure of poly(N-isopropyl-acrylamide-co-ATBA, denoted as PNI-co-ATBA. c Possible binding model of an ATBA functional monomer with three hydrogen phosphates (HPO4 2—) driven by H-bonding interactions, as indicated by green dashed lines with different bond lengths. This model was obtained from quantum chemistry calculation (Gaussian, density functional theory (DFT), at 6-311 G level of theory, solvent: H2O). d Hydrogen nuclear magnetic resonance (1H NMR) spectra of ATBA (A) upon additions of 0.5 (B), 1 (C), 2 (D) and 3 (E) equimolar amounts of HPO4 2— (tetrabutyl-ammonium as countercation) in deuterated dimethylsulphoxide at 20 °C. The chemical shift changes of ATBA protons (the attribution of each proton is shown in b) and HPO4 2— are indicated by blue dashed arrows/box or green inverted triangles, respectively. e pH-dependent association constant (K a) of ATBA bound to NMPs 1 and 2 and four serine PPs with mono-, di-, tri-, or tetra-phosphates (i.e., 1pS–4pS), the peptide sequences are shown in Fig. 2l. K a values were obtained from fluorescence titration experiments performed in various buffer solutions and these peptides were labelled with fluorescein at N terminus. f Temperature-dependent transmittance change of the copolymer aqueous solution at pH 3, 6.5 or 10, which indicated the good thermoresponsiveness and pH responsiveness of the copolymer. g Schematic of reversible overturn of copolymer chains and the corresponding binding/release towards MPPs modulated by solvent polarity. h Schematic of reversible coil-to-globule transition of copolymer chains and the binding/release of MPPs modulated by solution pH or temperature
