Virus capsids function as building blocks with the ability to form higher order three-dimensional array materials. In our laboratory, virus-like particles (VLPs) derived from bacteriophage P22 are studied. Decoration (Dec) protein, which binds to the exterior surface of P22 VLPs, is utilized as a linker protein to assist the P22 VLPs to achieve higher order assembly. P22 has two forms: procapsid (PC) form and expanded (Ex) form. It has been demonstrated that Dec can be used to facilitate assembly of P22 in Ex form; however, the original Dec protein cannot bind to the PC form. Because transformation from PC to Ex requires heat or chemical treatment, it is advantageous to mediate assembly of P22 PC for materials development such as enzyme encapsulated P22 arrays. The objective of this research, therefore, is to engineer Dec-based linker proteins to investigate the assembly of P22 in its PC form.

This investigation was initiated with computational modeling to evaluate protein structures which have affinity to P22 PC. The computational modeling suggests that a helix-turn-helix bundle (including gp41 core, 2L6HC3_13, and 5L6HC3_1) could exhibit high affinity to P22 PC. We then experimentally designed the three Dec-based linker proteins formulated on these computational predictions (Fig 1). We constructed plasmids for expressing the linker proteins genetically fused with Dec, purified these proteins from an E. coli expression system, and assessed their capability to bind to P22 PC. Preliminary results suggest that gp41 core with Dec is associated with P22 PC. We are currently modifying the protein to prepare a ditopic linker and assess its capability to mediate assembly of P22 PC into higher order assembly. We expect that integration of computational modeling and experimental verification will be a powerful approach to design protein linkers for controlled construction of protein array materials.

Figure 1. Computational models of helix-turn-helix Dec fusion proteins

Daisuke Kihara

Purdue University

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