title: Mechanical anisotropy of ankyrin repeats.
abstract: Red blood cells are frequently deformed and their cytoskeletal proteins such as spectrin and ankyrin-R are repeatedly subjected to mechanical forces. While the mechanics of spectrin was thoroughly investigated in vitro and in vivo, little is known about the mechanical behavior of ankyrin-R. In this study, we combine coarse-grained steered molecular dynamics simulations and atomic force spectroscopy to examine the mechanical response of ankyrin repeats (ARs) in a model synthetic AR protein NI6C, and in the D34 fragment of native ankyrin-R when these proteins are subjected to various stretching geometry conditions. Our steered molecular dynamics results, supported by AFM measurements, reveal an unusual mechanical anisotropy of ARs: their mechanical stability is greater when their unfolding is forced to propagate from the N-terminus toward the C-terminus (repeats unfold at ~60 pN), as compared to the unfolding in the opposite direction (unfolding force ∼ 30 pN). This anisotropy is also reflected in the complex refolding behavior of ARs. The origin of this unfolding and refolding anisotropy is in the various numbers of native contacts that are broken and formed at the interfaces between neighboring repeats depending on the unfolding/refolding propagation directions. Finally, we discuss how these complex mechanical properties of ARs in D34 may affect its behavior in vivo.
authors.affiliation: Center for Biologically Inspired Materials and Material Systems and Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina, USA.
authors.forename: Whasil
authors.initials: W
authors.lastname: Lee
authors.forename: Xiancheng
authors.initials: X
authors.lastname: Zeng
authors.forename: Kristina
authors.initials: K
authors.lastname: Rotolo
authors.forename: Ming
authors.initials: M
authors.lastname: Yang
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Schofield
authors.forename: Vann
authors.initials: V
authors.lastname: Bennett
authors.forename: Weitao
authors.initials: W
authors.lastname: Yang
authors.forename: Piotr E
authors.initials: PE
authors.lastname: Marszalek
mesh_terms: D000595:Amino Acid Sequence; D016880:Anisotropy; D017089:Ankyrin Repeat; D017487:Ankyrins / Q000737:chemistry; D001696:Biomechanical Phenomena; D004548:Elasticity; D055595:Mechanical Phenomena; D018625:Microscopy, Atomic Force; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D058849:Protein Refolding; D058767:Protein Unfolding
chemical_list: D017487:Ankyrins; D010446:Peptide Fragments