Design of protein struts for self-assembling nanoconstructs

Abstract

Bacteriophage T4 tail fibers have a quaternary structure of bent rigid rods, 3 x 160 nm in size. The four proteins which make up these organelles are able to self-assemble in an essentially irreversible manner. To use the self-assembly domains of these proteins as elements in construction of mesoscale structures, we must be able to rearrange these domains without affecting the self-assembly properties and add internal binding sites for other functional elements. Here we present results on several alterations of the P37 component of the T4 tail fiber that change its length and add novel protein sequences into the protein. One of these sequences is an antibody binding site that is used to inactivate phage carrying the modified gene.

Figure 1

Phage images. (A) Structure of bacteriophage T4. (B) Electron micrograph of T4 37SΔ1 phage. The white line next to the distal portion of the tail fiber indicates the length of a wild-type distal tail fiber at the same magnification. (C) Electron micrograph of T4 37SΔ1ras2 treated with mAb and secondary antiserum.

Figure 2

Inactivation of phage by a monoclonal antibody. (A) Treatment of phage with mAb and secondary anti-serum. Each phage type was treated with 1 μg of mAb as described in Materials and Methods. (B) Time course of mAb treatment. SΔ1ras2 phage were treated with 3 μg of mAb for the indicated time before a 30 min incubation with secondary anti-serum. (C) Dose-response study of SΔ1ras2 phage with varying amounts of mAb. (D) Effect of treating mAb with free epitope before inactivation of SΔ1ras2.

Figure 3

Self-assembly of fibers from tail fiber derived chimeric proteins. (A) Protein domains used to create a chimeric protein subunit (matured protein complexes shown). (B) Self-assembly of chimeric proteins onto a P37 initiator. The initiator is required to allow the gp36 monomer domains to combine to form the mature P36 domain. As in the wild-type fiber, this assembly propagates along the axis of the central rod domain. In the case of the chimeric proteins, this results in the formation of another P37 domain, supporting the next round of polymerization.