title: Direct observation of amyloid nucleation under nanomechanical stretching.
abstract: Self-assembly of amyloid nanofiber is associated with both functional biological and pathological processes such as those in neurodegenerative diseases. Despite intensive studies, the stochastic nature of the process has made it difficult to elucidate a molecular mechanism for the key amyloid nucleation event. Here we investigated nucleation of the silk-elastin-like peptide (SELP) amyloid using time-lapse lateral force microscopy (LFM). By repeated scanning of a single line on a SELP-coated mica surface, we observed a sudden stepwise height increase. This corresponds to nucleation of an amyloid fiber, which subsequently grew perpendicular to the scanning direction. The lateral force profiles followed either a worm-like chain model or an exponential function, suggesting that the atomic force microscopy (AFM) tip stretches a single or multiple SELP molecules along the scanning direction. The probability of nucleation correlated with the maximum stretching force and extension, implying that stretching of SELP molecules is a key molecular event for amyloid nucleation. The mechanically induced nucleation allows for positional and directional control of amyloid assembly in vitro, which we demonstrate by generating single nanofibers at predetermined nucleation sites.
authors.affiliation: Department of Materials Science and Engineering, ‡Fischell Department of Bioengineering, ¶Department of Mechanical Engineering, University of Maryland , College Park, Maryland 20742, United States.
authors.forename: Nitinun
authors.initials: N
authors.lastname: Varongchayakul
authors.forename: Sara
authors.initials: S
authors.lastname: Johnson
authors.forename: Trina
authors.initials: T
authors.lastname: Quabili
authors.forename: Joseph
authors.initials: J
authors.lastname: Cappello
authors.forename: Hamidreza
authors.initials: H
authors.lastname: Ghandehari
authors.forename: Santiago De Jesus
authors.initials: Sde J
authors.lastname: Solares
authors.forename: Wonmuk
authors.initials: W
authors.lastname: Hwang
authors.forename: Joonil
authors.initials: J
authors.lastname: Seog
mesh_terms: D058227:Amyloidogenic Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D003460:Crystallization / Q000379:methods*; D019281:Dimerization; D055119:Elastic Modulus; D008846:Micromanipulation / Q000379:methods*; D018625:Microscopy, Atomic Force / Q000379:methods*; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry* / Q000648:ultrastructure*; D013314:Stress, Mechanical
chemical_list: D058227:Amyloidogenic Proteins; D011993:Recombinant Fusion Proteins; C533248:silk-elastinlike protein 47K