Dahl T, Sabsay B, Veis A
Department of Basic and Behavioral Sciences, Division of Oral Biology, Northwestern University, 303 E. Chicago Ave., Chicago, Illinois, 60611, USA.
J Struct Biol. 1998 Oct;123(2):162-8. doi: 10.1006/jsbi.1998.4025.
It has been postulated that phosphophoryn (PP) molecules bind specifically to type I collagen fibrils as the key event in inducing matrix mineralization in dentin. The nature and specificity of the collagen molecule-PP interaction has been examined by rotary shadowing-electron microscopy of mixtures of native, monomeric lathyritic rat skin collagen and purified rat incisor PP. An antibody to the amino-telopeptide of the collagen alpha1(I)-chain was used to determine the N-terminal end of the collagen molecules. Solutions of collagen and PP in 0.01 M ammonium formate (+/- antibody) were mixed and spread in 70% glycerol-30% 0.01 M ammonium formate on freshly cleaved mica surfaces using the sandwich technique. After rotary shadowing with Pt and backcoating with a carbon film, the spreads were viewed in a JEOL 1200EX TEM. The PP appeared as 15-nm diameter globules, the collagen as semi-flexible 270 nm filaments. At neutral pH and low PP/collagen mixing ratios, a single interaction site was evident, centered at approximately 210 nm from the N-terminus. The binding interaction induced a local conformational change in the collagen, bending the molecule and reducing its effective length. The sequence within the collagen-PP-binding domain has a net-positive charge but contains both positively and negatively charged groups.
