title: Cross-linking by protein oxidation in the rapidly setting gel-based glues of slugs.
abstract: The terrestrial slug Arion subfuscus secretes a glue that is a dilute gel with remarkable adhesive and cohesive strength. The function of this glue depends on metals, raising the possibility that metal-catalyzed oxidation plays a role. The extent and time course of protein oxidation was measured by immunoblotting to detect the resulting carbonyl groups. Several proteins, particularly one with a relative molecular mass (M(r)) of 165 x 10³, were heavily oxidized. Of the proteins known to distinguish the glue from non-adhesive mucus, only specific size variants were oxidized. The oxidation appears to occur within the first few seconds of secretion. Although carbonyls were detected by 2,4-dinitrophenylhydrazine (DNPH) in denatured proteins, they were not easily detected in the native state. The presence of reversible cross-links derived from carbonyls was tested for by treatment with sodium borohydride, which would reduce uncross-linked carbonyls to alcohols, but stabilize imine bonds formed by carbonyls and thus lead to less soluble complexes. Consistent with imine bond formation, sodium borohydride led to a 20-35% decrease in the amount of soluble protein with a M(r) of 40-165 (x 10³) without changing the carbonyl content per protein. In contrast, the nucleophile hydroxylamine, which would competitively disrupt imine bonds, increased protein solubility in the glue. Finally, the primary amine groups on a protein with a M(r) of 15 x 10³ were not accessible to acid anhydrides. The results suggest that cross-links between aldehydes and primary amines contribute to the cohesive strength of the glue.
authors.affiliation: Department of Biology, Ithaca College, Ithaca, NY 14850, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Bradshaw
authors.forename: Michael
authors.initials: M
authors.lastname: Salt
authors.forename: Ashley
authors.initials: A
authors.lastname: Bell
authors.forename: Matt
authors.initials: M
authors.lastname: Zeitler
authors.forename: Noelle
authors.initials: N
authors.lastname: Litra
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Smith
mesh_terms: D000269:Adhesives / Q000737:chemistry / Q000378:metabolism*; D000447:Aldehydes / Q000737:chemistry / Q000378:metabolism; D000588:Amines / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001894:Borohydrides; D003432:Cross-Linking Reagents / Q000737:chemistry / Q000378:metabolism*; D049851:Gastropoda / Q000737:chemistry*; D005782:Gels / Q000737:chemistry / Q000378:metabolism*; D006834:Hydrazines; D019811:Hydroxylamine; D015151:Immunoblotting; D010084:Oxidation-Reduction; D011506:Proteins / Q000378:metabolism*
chemical_list: D000269:Adhesives; D000447:Aldehydes; D000588:Amines; D001894:Borohydrides; D003432:Cross-Linking Reagents; D005782:Gels; D006834:Hydrazines; D011506:Proteins; C446799:dinitrophenylhydrazine; D019811:Hydroxylamine; C025364:sodium borohydride