Abstract
A stable nonreducible trifunctional cross-linking amino acid has been isolated from mature bovine skin collagen fibrils. Previous cross-link peptide isolations and amino acid analyses indicate the compound has properties identical with those of hydroxyaldolhistidine. Its newly proposed structure was verified using fast atom bombardment mass spectrometry, and 1H and 13C nuclear magnetic resonance. The data indicated that the cross-link consists of the prosthetic groups from one residue each of histidine, hydroxylysine, and lysine. The 1H and 13C nuclear magnetic resonance data indicated that imidazole C-2 of histidine is linked to C-6 of norleucine (epsilon-deaminated lysine residue) which in turn is linked to the C-6 amino group of hydroxylysine. Based on the trivial names for other cross-linking residues found in collagen and elastin it was given the name histidinohydroxylysinonorleucine. In vitro incubation studies for up to 24 weeks, in aqueous solution at physiological pH and ionic strength, using 6-month-old bovine embryo skin demonstrated a one-to-one stoichiometric relationship between the disappearance of the labile reducible bifunctional cross-link dehydrohydroxylysinonorleucine and the appearance of histidinohydroxylsinonorleucine. These results can partially explain the previously observed disappearance of dehydrohydroxylysinonorleucine with chronological age.
Highlights
From the $Dental Research Center and **Department of Biochemistry, University of North Carolina at Chapel Hill, Cham1Hill
The 'H and 13Cnuclear magnetic resonancedata indicated that imidazole C-2 of histidine is linked toC6 of norleucine (e-deaminatedlysine residue) which in turn is linked to the C-6 amino group of hydroxylysine
Lecularly cross-linked chains of 3 to 1 at these locations indicated that the molecular packing structure of type I collagen in "skeletal" tissue is stereospecific in nature and the molecules in fibrils are packed with a specific azimuthal orientation (2)
Summary
1142611434,1987 Printed in U.S.A. Structure and Formation oaf Stable Histidine-based Trifunctional Cross-link in Skin Collagen*. These in turn stoichiand amino acid analyses indicate the compound has ometrically condense with the €-amino groups of Hyl-87 on properties identical with those of hydroxyaldolhisti- all three chainosf neighboring collagen molecules.The quandine. Its putative structure cubationstudies for up to 2 4 weeks, inaqueoussolution was proposed to be hydroxyaldolhistidine (HAH),'andits at physiological pH and ionic strength, using 6-month- speculated formation was by the condensation of the prosold bovine embryoskin demonstrateda one-to-one stoi- thetic groups of peptidyl residues of 5-amino-5-carboxypenchiometric relationship between the disappearance of tanal, 2-hydroxy-5-amino-5-carboxypentanaa1n,d the imidathe labile reducible bifunctional cross-link dehydro- zole N-3 of histidine (3). Further chromatographic procedures, we isolated an apparently homogeneous three-chained peptide containing the putative HAH cross-link from type I bovine skin collagen (4)
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