A thermo-responsive, self-assembling biointerface for on demand release of surface-immobilised proteins

Abstract

Dedicated chemistries for on-demand capture and release of biomolecules at the solid–liquid interface are required for applications in drug delivery, for the synthesis of switchable surfaces used in analytical devices and for the assembly of next-generation biomaterials with complex architectures and functions. Here we report the engineering of a binary self-assembling polypeptide system for reversible protein capture, immobilisation and controlled thermo-responsive release from a solid surface. The first element of the binary system is a universal protein substrate immobilised on a solid surface. This protein is bio-inspired by the neuronal SNAP25, which is the protein involved in the docking and fusion of synaptic vesicles to the synaptic membrane. The second element is an artificial chimeric protein engineered to include distinct domains from three different proteins: Syntaxin, VAMP and SNAP25. These native proteins constitute the machinery dedicated to vesicle trafficking in eukaryotes. We removed approximately 70% of native protein sequence from these proteins and constructed a protein chimera capable of high affinity interaction and self-assembly with immobilised substrate. The interaction of the two parts of the engineered protein complex is strong but fully-reversible and therefore the chimera can be recombinantly fused as a tag to a protein of interest, to allow spontaneous assembly and stimuli-sensitive release from the surface upon heating at a predetermined temperature. Two thermo-responsive tags are reported: the first presents remarkable thermal stability with melting temperature of the order of 80 °C; the second disassembles at a substantially lower temperature of about 45 °C. The latter is a promising candidate for remote-controlled localised delivery of therapeutic proteins, as physiologically tolerable local increase of temperatures in the 40–45 °C range can be achieved using magnetic fields, infra-red light or focused ultrasound. Importantly, these two novel polypeptides provide a broader blueprint for the engineering of future functional proteins with predictable folding and response to external stimuli.