Self-assembly of avidin and D-biotin-tethering zeolite microcrystals into fibrous aggregates

Avidin and nanometer-sized zeolite crystals (∼300 nm) tethered with D-biotin readily self-assemble into thin (2-20 μm) and very long (>1 cm) fibrous aggregates in a buffer solution of pH = 7.4 when the avidin-to-zeolite weight ratio (A/Z) is equal to or higher than 0.2. At A/Z = 0.2, the exteriors of the produced fibrils are covered with zeolite-A crystals. At A/Z = 0.4, the zeolite crystals are completely buried within the fibrils covered with thick layers of avidin. At A/Z = 0.8-1.0, the morphology of the fibrils becomes smooth and flat due to the thick surface-lining avidin layers. The zeolite and avidin remain intact within the fibrils. Control experiments reveal that complexation between avidin and the zeolite-bound biotin is essential for fibrillation to occur. Interestingly, discrete clusters of zeolite crystals with sizes of 5-10 μm are produced when the A/Z ratio is reduced to 0.1. The observed fibrillation is very much like the previously reported case with β-glucosidase and D-glucose-tethering zeolite microcrystals, despite that the type of the protein-substrate pair is different. This result therefore raises the possibility that self-assembly of complexforming proteins and the nanoparticles or microparticles tethered with the corresponding substrates into fibrils is a general phenomenon.