The group of CAO Yu used the capsid protein (HaCP) of Baculovirus expressed by E. coli and found by cryo-electron microscopy that a variety of exogenous proteins expressed at the N-terminus of HaCP could be directly fused and displayed on the outer surface. HaCP had two forms of assembly in vitro: one with a small diameter named N-tube, and another with a relatively large diameter, named W-tube. The N-tube is a helical structure similar to the TMV capsid, with 111/3 protein subunits arranged in a spiral along each circle. The W-tube is a stack of disc structures consisting of 12 protein subunits with a 11.25° rotation between adjacent discs. The interaction between the HaCP nanotube subunits was tunable, leading to high flexibility of the resulting nanotubes. HaCP nanotubes thus allow to accommodate larger guest compounds compared to assembled subunits of TMVs and thus might be evolved into nanoscale functional molecules.
CAS news release, July 30, 2018