Crystallization of Fc_Ankyrin repeat complex

Abstract

The ankyrin repeat is one of the most frequently observed amino acid motifs in protein databases. Ankyrin repeat act as building blocks that stack side by side, forming underlying architecture, specific protein-binding interface. This protein-protein interaction module is involved in a diverse set of cellular functions. The modular nature of ankyrin repeat proteins suggests assembling repeat domains module-wise. Designed ankyrin repeat protein library was generated by a strategy that exploits repetitive modular architecture for the generation of combinatorial libraries of repeat proteins with novel binding specificities. Ankyrin repeat protein, which is a specific binder against the Fc domain of human IgG1 was founded. When IgG is subjected to proteolytic cleavage, several fragments are produced. If the enzyme is papain used to cleave IgG, two major types of fragments are obtained. One fragment binds antigen is referred to as Fab (fragment antigen-binding). The other fragment, known as Fc (fragment crystallizable), does not bind antigen but activates a molecular pathway known as complement and has various biological effector functions, such as the ability to bind to receptors found on macrophages and various other cells. Fc domain of human IgG1 is composed of two identical, disulfied linked peptides containing the heavy chain $C_H2$ and $C_H3$ domains. Fc has a propensity to self-associate and to crystallize into a lattice. The molecule most likely forms homodimers. We expect that Fc_ankyrin repeat protein complex would be a potential scaffold to make protein polymer by elongation number of internal ankyrin repeat or binding with other designed proteins to the complex. To determine the structure of Fc_ankyrin repreat protein complex, crystallization of Fc_ankyrin repeat protein complex was tried. In this paper, the crystal of ankyrin repeat protein, binder against Fc domain of human IgG1, was obtained and forming Fc_ankyrin repeat protein complex was verified. ...