title: Collagen insulated from tensile damage by domains that unfold reversibly: in situ X-ray investigation of mechanical yield and damage repair in the mussel byssus.
abstract: The byssal threads of the California mussel, Mytilus californianus, are highly hysteretic, elastomeric fibers that collectively perform a holdfast function in wave-swept rocky seashore habitats. Following cyclic loading past the mechanical yield point, threads exhibit a damage-dependent reduction in mechanical performance. However, the distal portion of the byssal thread is capable of recovering initial material properties through a time-dependent healing process in the absence of active cellular metabolism. Byssal threads are composed almost exclusively of multi-domain hybrid collagens known as preCols, which largely determine the mechanical properties of the thread. Here, the structure-property relationships that govern thread mechanical performance are further probed. The molecular rearrangements that occur during yield and damage repair were investigated using time-resolved in situ wide-angle X-ray diffraction (WAXD) coupled with cyclic tensile loading of threads and through thermally enhanced damage-repair studies. Results indicate that the collagen domains in byssal preCols are mechanically protected by the unfolding of sacrificial non-collagenous domains that refold on a slower time-scale. Time-dependent healing is primarily attributed to stochastic recoupling of broken histidine-metal coordination complexes.
authors.affiliation: Dept. of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara 93106, USA. Matt.Harrington@mpikg.mpg.de
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Harrington
authors.forename: Himadri S
authors.initials: HS
authors.lastname: Gupta
authors.forename: Peter
authors.initials: P
authors.lastname: Fratzl
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000818:Animals; D003094:Collagen / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology*; D008954:Models, Biological; D049878:Mytilus / Q000378:metabolism*; D013718:Tensile Strength / Q000502:physiology*; D014961:X-Ray Diffraction
chemical_list: D003094:Collagen