Article info 2018 6 (1)    006  (01)   pp.  10 ~ 14
Title Application of helix fusion method in structural biology
Authors Jin Hong Kim and Jie-Oh Lee*
Institutions Department of Chemistry, KAIST, Daejeon, Korea, Department of Chemistry, KAIST, 291 Daehak-no, Yuseong-gu, Daejeon 34141, Korea *Correspondence: jieoh@kaist.ac.kr
Abstract Generating artificial protein assemblies with complex shapes requires a method of connecting protein components with stable and predictable structures. Because they have uniform structures, alpha helices can provide an excellent linker for connecting proteins with predictable structures. However, except for a few exceptional cases, early attempts to ligate two proteins by fusion of terminal alpha helices were not successful. In order to solve this problem, several new methods have been developed in recent years. In the chemical cross-linker method, the linker helix is stabilized by a chemical cross-linker that can force an alpha helical geometry by fixing the distance between two cysteine residues. In the shared-helix method, the linker helix is generated by overlapping pairs of alpha helices by 1~2 turns using a molecular modeling program. The amino acid sequence at the overlapped site is chosen from the two natural sequences that would stabilize the alpha helical linker. These two helix fusion methods are expected to be useful in structural biology because they can enhance the crystallization property of challenging target proteins by providing a rigid and crystallizable surface. They also can be used to produce artificial protein complexes by connecting the target protein to a large backbone protein. The resulting protein complex effectively increases the size of the target protein for cryo-electron microscopy study. In this review, we summarize recent progress of the helix fusion methods and their application to structural study of challenging proteins.