title: Evidence of mineralization activity and supramolecular assembly by the N-terminal sequence of ACCBP, a biomineralization protein that is homologous to the acetylcholine binding protein family.
abstract: Several biomineralization proteins that exhibit intrinsic disorder also possess sequence regions that are homologous to nonmineral associated folded proteins. One such protein is the amorphous calcium carbonate binding protein (ACCBP), one of several proteins that regulate the formation of the oyster shell and exhibit 30% conserved sequence identity to the acetylcholine binding protein sequences. To gain a better understanding of the ACCBP protein, we utilized bioinformatic approaches to identify the location of disordered and folded regions within this protein. In addition, we synthesized a 50 AA polypeptide, ACCN, representing the N-terminal domain of the mature processed ACCBP protein. We then utilized this polypeptide to determine the mineralization activity and qualitative structure of the N-terminal region of ACCBP. Our bioinformatic studies indicate that ACCBP consists of a ten-stranded beta-sandwich structure that includes short disordered sequence blocks, two of which reside within the primarily helical and surface-accessible ACCN sequence. Circular dichroism studies reveal that ACCN is partially disordered in solution; however, ACCN can be induced to fold into an alpha helix in the presence of TFE. Furthermore, we confirm that the ACCN sequence is multifunctional; this sequence promotes radial calcite polycrystal growth on Kevlar threads and forms supramolecular assemblies in solution that contain amorphous-appearing deposits. We conclude that the partially disordered ACCN sequence is a putative site for mineralization activity within the ACCBP protein and that the presence of short disordered sequence regions within the ACCBP fold are essential for function.
authors.affiliation: Center for Biomolecular Materials Spectroscopy, Laboratory for Chemical Physics, New York University, 345 East 24th Street, New York, New York 10010, USA.
authors.forename: Fairland F
authors.initials: FF
authors.lastname: Amos
authors.forename: Moise
authors.initials: M
authors.lastname: Ndao
authors.forename: John Spencer
authors.initials: JS
authors.lastname: Evans
mesh_terms: D000109:Acetylcholine / Q000737:chemistry*; D000595:Amino Acid Sequence; D000818:Animals; D002113:Calcification, Physiologic; D002119:Calcium Carbonate / Q000737:chemistry*; D019295:Computational Biology; D003460:Crystallization; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry; D049911:Pinctada / Q000378:metabolism / Q000502:physiology*; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid
chemical_list: D010455:Peptides; D011978:Receptors, Nicotinic; D002119:Calcium Carbonate; D000109:Acetylcholine