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Loss of biological control of enamel mineralization in amelogenin-phosphorylation-deficient mice

Journal Article · · Journal of Structural Biology
 [1];  [2];  [3];  [2];  [2]
  1. Univ. of Wisconsin, Madison, WI (United States)
  2. Univ. of Pittsburgh, PA (United States)
  3. Univ. of Wisconsin, Madison, WI (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Amelogenin, the most abundant enamel matrix protein, plays several critical roles in enamel formation. Importantly, we previously found that the singular phosphorylation site at Ser16 in amelogenin plays an essential role in amelogenesis. Studies of genetically knock-in (KI) modified mice in which Ser16 in amelogenin is substituted with Ala that prevents amelogenin phosphorylation, and in vitro mineralization experiments, have shown that phosphorylated amelogenin transiently stabilizes amorphous calcium phosphate (ACP), the initial mineral phase in forming enamel. Furthermore, KI mice exhibit dramatic differences in the enamel structure compared with wild type (WT) mice, including thinner enamel lacking enamel rods and ectopic surface calcifications. Here, we now demonstrate that amelogenin phosphorylation also affects the organization and composition of mature enamel mineral. In this work, we compared WT, KI, and heterozygous (HET) enamel and found that in the WT elongated crystals are co-oriented within each rod, however, their c-axes are not aligned with the rods' axes. In contrast, in rod-less KI enamel, crystalline c-axes are less co-oriented, with misorientation progressively increasing toward the enamel surface, which contains spherulites, with a morphology consistent with abiotic formation. Furthermore, we found significant differences in enamel hardness and carbonate content between the genotypes. ACP was also observed in the interrod of WT and HET enamel, and throughout aprismatic KI enamel. In conclusion, amelogenin phosphorylation plays crucial roles in controlling structural, crystallographic, mechanical, and compositional characteristics of dental enamel. Thus, loss of amelogenin phosphorylation leads to a reduction in the biological control over the enamel mineralization process.
Research Organization:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
Sponsoring Organization:
National Institutes of Health (NIH), National Institute of Dental and Craniofacial Research (NIDCR); National Science Foundation (NSF); USDOE Laboratory Directed Research and Development (LDRD) Program; USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division
Grant/Contract Number:
AC02-05CH11231; FG02-07ER15899
OSTI ID:
1963451
Journal Information:
Journal of Structural Biology, Journal Name: Journal of Structural Biology Journal Issue: 2 Vol. 214; ISSN 1047-8477
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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