title: Halogenated veneers: protein cross-linking and halogenation in the jaws of nereis, a marine polychaete worm.
abstract: Mineralized tissues are produced by most living organisms for load and impact functions. In contrast, the jaws of the clam worm, Nereis, are hard without mineralization. However, they are peculiarly rich in halogens, which are associated with a variety of post-translationally modified amino acids, many of which are multiply halogenated by chlorine, bromine, and/or iodine. Several of these modified amino acids, namely dibromohistidine, bromoiodohistidine, chloroiodotyrosine, bromoiodotyrosine, chlorodityrosine, chlorotrityrosine, chlorobromotrityrosine, and bromoiodotrityrosine, have not been previously reported. We have found that the distributions of Cl, Br, and I differ: Cl is widespread whereas Br and I, although not colocalized, are concentrated in proximity to the external jaw surfaces. By using nanoindentation, we show that Br and I are unlikely to play a purely mechanical role, but that the local Zn and Cl concentrations and jaw microstructure are the prime determinants of local jaw hardness. Several of the post-translationally modified amino acids are akin to those found in various sclerotized structures of invertebrates, and we propose that they are part of a cross-linked protein casing.
authors.affiliation: Department Chemistry and Biochemistry, University of California, Santa Barbara, CA 93106, USA.
authors.forename: Henrik
authors.initials: H
authors.lastname: Birkedal
authors.forename: Rashda K
authors.initials: RK
authors.lastname: Khan
authors.forename: Nelle
authors.initials: N
authors.lastname: Slack
authors.forename: Chris
authors.initials: C
authors.lastname: Broomell
authors.forename: Helga C
authors.initials: HC
authors.lastname: Lichtenegger
authors.forename: Frank
authors.initials: F
authors.lastname: Zok
authors.forename: Galen D
authors.initials: GD
authors.lastname: Stucky
authors.forename: J Herbert
authors.initials: JH
authors.lastname: Waite
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001696:Biomechanical Phenomena; D001966:Bromine / Q000032:analysis; D002713:Chlorine / Q000032:analysis; D004577:Electron Probe Microanalysis; D006219:Halogens / Q000032:analysis / Q000378:metabolism*; D006244:Hardness; D006639:Histidine / Q000031:analogs & derivatives / Q000032:analysis; D006868:Hydrolysis; D007455:Iodine / Q000032:analysis; D007568:Jaw / Q000033:anatomy & histology / Q000737:chemistry / Q000378:metabolism*; D013058:Mass Spectrometry; D011077:Polychaeta / Q000378:metabolism* / Q000502:physiology; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000737:chemistry / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000032:analysis; D015032:Zinc / Q000032:analysis
chemical_list: D000596:Amino Acids; D006219:Halogens; D011506:Proteins; C101095:trityrosine; D014443:Tyrosine; D006639:Histidine; D002713:Chlorine; D007455:Iodine; C007543:dityrosine; D015032:Zinc; D001966:Bromine