title: Molecular dynamics study of the stabilities of consensus designed ankyrin repeat proteins.
abstract: Two designed ankyrin repeat (AR) proteins (E3_5 and E3_19) are high homologous (with about 87% sequence identity) and their crystal structures have a Calpha atom-positional root-mean-square difference of about 0.14 nm. However, it was found that E3_5 is considerably more stable than E3_19 in guanidinium hydrochloride and thermal denaturation experiments. With the goal of providing insights into the various factors contributing to the stabilities of the designed AR proteins and suggesting possible mutations to enhance their stabilities, homology modeling and molecular dynamics (MD) simulations with explicit solvent have been performed. Because the crystal structure of E3_19 was solved later than that of E3_5, a homology model of E3_19 based on the crystal structure of E3_5 was also used in the simulations. E3_5 shows a very stable trajectory in both crystal and solution simulations. In contrast, the C-terminal repeat of E3_19 unfolds in the simulations starting from either the modeled structure or the crystal structure, although it has a sequence identical to that of E3_5. A continuum electrostatic model was used to estimate the effect of single mutations on protein stability and to study the interaction between the internal ARs and the C-terminal capping AR. Mutations involving charged residues were found to have large effects on stability. Due to the difference in charge distribution in the internal ARs of E3_19 and E3_5, their interaction with the C-terminal capping AR is less favorable in E3_19. The simulation trajectories suggest that the stability of the designed AR proteins can be increased by optimizing the electrostatic interactions within and between the different repeats.
authors.affiliation: Laboratory of Physical Chemistry, Swiss Federal Institute of Technology Zürich, ETH Hönggerberg, Zürich, Switzerland.
authors.forename: Haibo
authors.initials: H
authors.lastname: Yu
authors.forename: Andreas
authors.initials: A
authors.lastname: Kohl
authors.forename: H Kaspar
authors.initials: HK
authors.lastname: Binz
authors.forename: Andreas
authors.initials: A
authors.lastname: Plückthun
authors.forename: Markus G
authors.initials: MG
authors.lastname: Grütter
authors.forename: Wilfred F
authors.initials: WF
authors.lastname: van Gunsteren
mesh_terms: D017089:Ankyrin Repeat; D019295:Computational Biology; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D008958:Models, Molecular; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D011506:Proteins