Entrapment of N-terminal 6× His tagged rGFP (rGFP H , ThermoFisher), and rGFP lacking a His-tag (rGFP, Sigma Aldrich), within NTA functionalized C-star networks was characterized using a confocal microscopy assay with the same confocal setup as for solute penetration assays. An Ar-ion laser (488 nm) was used for excitation. Crystals prepared and extracted as described previously were first washed in order to remove EDTA present in the incubation buffer. This was achieved by 5 rounds of centrifugation, supernatant removal, and addition and mixing with washing buffer, WB (10 mM tris, 300 mM NaCl, pH 8.0). For imaging, a small volume (approx. 5 µL) of washed crystals was added to a glass microwell slide. Ni 2+ ions were introduced by addition of 10 µL NiCl 2 containing WB (10 mM NiCl 2 , WB). After allowing to incubate for 1 hour, excess Ni 2+ was removed by 5 rounds of washing. Each washing step involved the removal of 10 µL of solution from the well, addition of 10 µL of fresh WB, and thorough mixing by pipette aspiration. A 5 minute rest between washing steps was included to allow any dispersed crystals to sediment. After the final wash step, 5 µL of either rGFP H incubation buffer (7 µM rGFP H , 1 mg ml -1 bovine serum albumin (BSA), WB), or rGFP incubation buffer (7 µM rGFP, 1 mg ml -1 bovine serum albumin (BSA), WB) was added. Following a 1 hour incubation, excess protein was removed by 5 rounds of washing with WB. For the demonstration of the reversibility of protein binding (Fig. ), bound rGFP H was removed by 5 rounds of cleaning with EDTA containing washing buffer (1 mM EDTA, WB). Following this, crystals could be recharged with rGFP H by repeating the same washing, nickelation, and rGFP H addition steps detailed above. Between washing steps and during incubation periods, sample chambers were sealed with DNase free tape to prevent evaporation. Fluorescent and bright field confocal micrographs taken at the equatorial plane of crystals were obtained throughout the process. The degree of protein binding was estimated by taking the mean fluorescent intensity within the crystals, I Fluo , through manual masking of objects using the BioFormats plugin for ImageJ. Small angle X-ray scattering SAXS measurements were performed at the I22 beamline of the Diamond Light Source using a radiation wavelength of λ = 1 Å, and beam dimensions of approximately 300 µm wide × 100 µm high. The accessible q range was between 5×10 -3 and 0.56 Å -1 . Here the scattering q vector is defined as q = (4π/λ) sin θ ≡ 2π/d, where d is the d-spacing, 2θ is the scattering angle. The q-scale was calibrated using silver behenate, which has a well defined layer spacing of 58.38 Å. C-star crystals were prepared in capillaries as described above. The content of 6 capillaries per sample was extracted and concentrated by centrifugation and supernatant removal to a final C-star concentration of ∼ 100 µM. Concentrated C-Star samples were injected into borosilicate glass X-ray capillaries (diameter 1.6 mm) and left to sediment until a clear pellet became visible. Measurements were taken by scanning the X-ray beam across the sample near the pellet region, taking 1 frame per location with an exposure time of 100 ms. Averaged diffraction patterns were built up from at least 20 locations per sample. Background subtraction was performed in two steps for the SAXS patterns shown in Fig. , Fig. and Fig. . Measured scattering from the buffer was first subtracted, followed by subtraction of an arbitrary logarithmic background to account for variable scattering between glass capillaries. For experiments on trigger-induced isothermal melting (Fig. ), after an initial measurement, a volume of trigger strand approximately corresponding to a 1:1 molar ratio of trigger:bridge strand was carefully added at the top of the capillary and allowed to passively diffuse throughout the sample. Measurements were taken as for previous samples, with identical scan locations for all time points. Between measurements, care was taken not to move the capillary in order to allow for direct comparison of the same pellet region over time. For experiments of protein binding in NTA functionalized networks, the same washing and rGFP H addition steps as described for the confocal binding assay were used. Here, fresh buffer addition and washing was performed with gel-loading pipette tips (Corning R ) to allow for thorough mixing and more efficient buffer extraction from narrow x-ray capillaries.