Engineering of brick and staple components for ordered assembly of synthetic repeat proteins.

Synthetic ɑRep repeat proteins are engineered as Brick and Staple protein pairs that together self-assemble into helical filaments. In most cases, the filaments spontaneously form supercrystals. Here, we describe an expanded series of ɑRep Bricks designed to stabilize the interaction between consecutive Bricks, to control the length of the assembled multimers, or to alter the spatial distribution of the Staple on the filaments. The effects of these Brick modifications on the assembly, on the final filament structure and on the crystal symmetry are analyzed by biochemical methods, electron microscopy and small angle X-ray scattering. We further extend the concept of Brick/Staple protein origami by designing a new type of "Janus"-like Brick protein that is equally assembled by orthogonal staples binding its inner or outer surfaces and thus ending inside or outside the filaments. The relative roles of longitudinal and lateral associations in the assembly process are discussed. This set of results demonstrates important proofs-of-principle for engineering these remarkably versatile proteins toward nanometer-to-micron scale constructions.