A C-RING-like domain participates in protein self-assembly and mineral nucleation

Biochemistry. 2011 Oct 18;50(41):8880-7. doi: 10.1021/bi201346d. Epub 2011 Sep 26.


AP7 is a nacre-associated protein of the mollusk shell that forms supramolecular assemblies that nucleate single-crystal aragonite in vitro. AP7 possesses two major sequence regions: a random coil 30-amino acid N-terminal domain (AP7N) and a partially disordered 36-amino acid C-terminal domain (AP7C) that exhibits imperfect sequence homology to the C subclass of the intracellular RING domain family. We report here new findings that implicate the C-RING domain in AP7-mediated supramolecular assembly and single-crystal mineral formation. AP7 protein spontaneously self-assembles over a pH range of 4-9 and is monomeric at pH >9.5. AP7N and AP7C both oligomerize over the pH range of 4-9, with the AP7C sequence closely resembling AP7 in terms of particle morphology and size. In vitro mineralization experiments demonstrate that both AP7N and AP7C form supramolecular assemblies that nucleate single-crystal calcium carbonates. Comparison of previously published nuclear magnetic resonance-based structures of AP7C and AP7N reveals the significant presence of complementary anionic-cationic electrostatic molecular surfaces on AP7C that are not found on AP7N, and this may explain the noted discrepancies between the two domains in terms of self-assembly and single-crystal nucleation. We conclude that the C-RING-like sequence is an important site for AP7 self-association and mineral nucleation, and this represents the first known instance of a RING-like sequence performing these functions within an extracellular protein.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Anions
  • Calcium Carbonate / chemistry
  • Carrier Proteins / chemistry*
  • Cations
  • Hydrogen-Ion Concentration
  • Light
  • Magnetic Resonance Spectroscopy / methods
  • Microscopy, Electron, Transmission / methods
  • Minerals / chemistry
  • Mollusca
  • Nacre / chemistry*
  • Protein Structure, Tertiary
  • Proteins / chemistry
  • Scattering, Radiation
  • Static Electricity


  • Anions
  • Carrier Proteins
  • Cations
  • Minerals
  • Nacre
  • Proteins
  • Calcium Carbonate