R.P. Watson; M.T. Christen; C. Ewald; F. Bumbak; C. Reichen; M. Mihajlovic; E. Schmidt; P. Güntert; A. Caflisch; A. Plückthun; O. Zerbe

Journal: Structure
Year: 2014
Volume: 22
Issue: 7
Pages: 985-995
DOI: 10.1016/j.str.2014.05.002
Type of Publication: Journal Article

Armadillo Domain Proteins; molecular dynamics; Protein Engineering; Protein Folding; repeat proteins; spontaneous assembly


Repeat proteins are built of modules, each of which constitutes a structural motif. We have investigated whether fragments of a designed consensus armadillo repeat protein (ArmRP) recognize each other. We examined a split ArmRP consisting of an N-capping repeat (denoted Y), three internal repeats (M), and a C-capping repeat (A). We demonstrate that the C-terminal MA fragment adopts a fold similar to the corresponding part of the entire protein. In contrast, the N-terminal YM2 fragment constitutes a molten globule. The two fragments form a 1:1 YM2:MA complex with a nanomolar dissociation constant essentially identical to the crystal structure of the continuous YM3A protein. Molecular dynamics simulations show that the complex is structurally stable over a 1 μs timescale and reveal the importance of hydrophobic contacts across the interface. We propose that the existence of a stable complex recapitulates possible intermediates in the early evolution of these repeat proteins.