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Hierarchical and Helical Self-Assembly of ADP-Ribosyl Cyclase into Large-Scale Protein Microtubes

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journal contribution
posted on 27.11.2008, 00:00 by Qun Liu, Irina A. Kriksunov, Zhongwu Wang, Richard Graeff, Hon Cheung Lee, Quan Hao
Proteins are macromolecules with characteristic structures and biological functions. It is extremely challenging to obtain protein microtube structures through self-assembly as proteins are very complex and flexible. Here we present a strategy showing how a specific protein, ADP-ribosyl cyclase, helically self-assembles from monomers into hexagonal nanochains and further to highly ordered crystalline microtubes. The structures of protein nanochains and consequently self-assembled superlattice were determined by X-ray crystallography at 4.5 Å resolution and imaged by scanning electron microscopy. The protein initially forms into dimers that have a fixed size of 5.6 nm, and then, helically self-assembles into 35.6 nm long hexagonal nanochains. One such nanochain consists of six dimers (12 monomers) that stack in order by a pseudo P61 screw axis. Seven nanochains produce a series of large-scale assemblies, nanorods, forming the building blocks for microrods. A proposed aging process of microrods results in the formation of hollow microstructures. Synthesis and characterization of large scale self-assembled protein microtubes may pave a new pathway, capable of not only understanding the self-assembly dynamics of biological materials, but also directing design and fabrication of multifunctional nanobuilding blocks with particular applications in biomedical engineering.