Exploring a Role in Tanning for the Gap Region of the Collagen Fibril: Catechin-Collagen Interactions

Authors: Brown, Eleanor - Ellie; Qi, Phoebe

Submitted to: Journal of American Leather Chemists Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2008
Publication Date: 9/1/2008
Citation: Brown, E.M., Qi, P.X. 2008. Exploring a Role in Tanning for the Gap Region of the Collagen Fibril: Catechin-Collagen Interactions. Journal of American Leather Chemists Association. 103(9):290-297.

Interpretive Summary: Tanning of animal hides produces leather, the highest value coproduct of the meat industry. Tanning stabilizes the protein (collagen) structure of the hide and imparts heat stability, enhanced tensile properties, and resistance to microbial degradation. Currently most high quality leather is "chrome-tanned," produced by treatment of the hide with salts of the mineral chromium. Because of environmental considerations, and customer preference, there is interest in developing new chrome-free tannages. The art of tanning with chromium salts, vegetable tannins or synthetic organic materials is highly developed, but the mechanisms are poorly understood. This study uses our previously reported computerized model of the collagen microfibril, the supermolecular protein component of hides and skins, to explore the interactions of catechin, a vegetable tannin, with collagen. Models of the catechin molecule were inserted into the collagen microfibril model and conditions typical of tanning were simulated. Under these conditions each catechin molecule moved relative to the collagen model into a position where a stabilizing bond might be formed. New information concerning the probable mechanism of vegetable tannins with collagen was obtained. The method will be valuable in predicting the effectiveness of proposed new tanning agents.

Technical Abstract: Electron micrographs of stained collagen fibrils display a pattern of alternating light and dark bands perpendicular to the axis of the collagen fibril. Light bands correspond to regions of more dense lateral packing where adjacent collagen monomers overlap, and dark bands correspond to 'gap' regions, domains of low-density molecular packing. Most studies of artificially stabilized collagen focus on crosslinks that utilize specific amino acid side chains, without considering whether these are more likely to be located in overlap or gap regions. The gap region with its lower molecular density, greater length, and available telopeptides appears promising as an area able to accommodate oligomeric compounds that are the typical tanning agents. This study uses the ERRC collagen microfibril model to explore the interactions of catechin, a model for vegetable tanning agents thought to interact with serine residues, in the collagen microfibril. Attempts at placing catechin near serine residues in the overlap region were not successful. Four catechin molecules were docked near serine residues in the gap region of the microfibril and subjected to conditions typical of tanning. Under these conditions each catechin molecule moved into a position where stabilizing bond formation was likely, although not with serine. The method will be valuable in predicting the effectiveness of proposed new tanning agents.