Probing the organic-mineral interface at the molecular level in model biominerals.
It is widely known that macromolecules, such as proteins, can control the nucleation and growth of inorganic solids in biomineralizing organisms. However, what is not known are the complementary molecular interactions, organization, and rearrangements that occur when proteins interact with inorganic solids during the formation of biominerals. The organic-mineral interface (OMI) is expected to be the site for these phenomena, and is therefore extraordinarily interesting to investigate. In this report, we employ X-ray absorption near edge (XANES) spectromicroscopy to investigate the electronic structure of both calcium carbonate mineral crystals and polypeptides, and detect changing bonds at the OMI during crystal growth in the presence of polypeptides. We acquired XANES spectra from calcium carbonate crystals grown in the presence of three mollusk nacre-associated polypeptides (AP7N, AP24N, n16N) and in the presence of a sea urchin spicule matrix protein, LSM34. All these model biominerals gave similar results, including the disruption of CO bonds in calcite and enhancement of the peaks associated with C-H bonds and C-O bonds in peptides, indicating ordering of the amino acid side chains in the mineral-associated polypeptides and carboxylate binding. This is the first evidence of the mutual effect of calcite on peptide chain and peptide chain on calcite during biomineralization. We also show that these changes do not occur when Asp and Glu are replaced in the n16N sequence with Asn and Gln, respectively, demonstrating that carboxyl groups in Asp and Glu do participate in polypeptide-mineral molecular associations.
Metzler
Rebecca A
RA
Department of Physics, University of Wisconsin-Madison, 1150 University Avenue, Madison, Wisconsin 53706, USA.
Kim
Il Won
IW
Delak
Katya
K
Evans
John Spencer
JS
Zhou
Dong
D
Beniash
Elia
E
Wilt
Fred
F
Abrecht
Mike
M
Chiou
Jau-Wern
JW
Guo
Jinghua
J
Coppersmith
Susan N
SN
Gilbert
P U P A
PU
D000595:Amino Acid Sequence; D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry*; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000302:isolation & purification; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D014965:X-Rays
D016326:Extracellular Matrix Proteins; C445339:LSM34 protein, Lytechinus pictus; D010455:Peptides; D002119:Calcium Carbonate