Rop protein

Rop (also known as repressor of primer) is a small homodimeric four-helix bundle protein formed by the antiparalell interaction of two helix-turn-helix monomers. The protein is expressed in E. coli as a mechanism for regulating the gene copy numbers of plasmids. The Rop protein's structure has been solved to high resolution. Due to its small size and known structure, Rop has been used in protein design work to rearrange its helical topology and reengineer its loop regions. In general, the four-helix bundle has been extensively used in de novo protein design work as a simple model to understand the relationship between protein sequence and structure.