title: In vitro effects of recombinant otoconin 90 upon calcite crystal growth. Significance of tertiary structure.
abstract: Otoconia are biomineral particles of microscopic size essential for perception of gravity and maintenance of balance. Millions of older Americans are affected in their mobility, quality of life and in their health by progressive demineralization of otoconia. Currently, no effective means to prevent or counteract this process are available. Because of prohibitive anatomical and biological constraints, otoconial research is lagging far behind other systems such as bone and teeth. We have overcome these obstacles by generating otoconial matrix proteins by recombinant techniques. In the present study, we evaluated the effects of recombinant Otoconin 90 (OC90), the principal soluble matrix protein upon calcite crystal growth patterns in vitro. Our findings highlight multiple effects, including facilitation of nucleation, and inhibition of crystal growth in a concentration-dependent manner. Moreover, OC90 induces morphologic changes characteristic of native otoconia. OC90 is considerably less acidic than the prototypical invertebrate CaCO(3) -associated protein, but is nevertheless an effective modulator of calcite crystal growth. Based on homology modeling of the sPLA2-like domains of OC90, we propose that the lower density of acidic residues of the primary sequence is compensated by formation of major anionic surface clusters upon folding into tertiary conformation.
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Washington University School of Medicine, St Louis, MO 63110, USA. luwenfu@gmail.com
authors.forename: Wenfu
authors.initials: W
authors.lastname: Lu
authors.forename: Dan
authors.initials: D
authors.lastname: Zhou
authors.forename: John J
authors.initials: JJ
authors.lastname: Freeman
authors.forename: Isolde
authors.initials: I
authors.lastname: Thalmann
authors.forename: David M
authors.initials: DM
authors.lastname: Ornitz
authors.forename: Ruediger
authors.initials: R
authors.lastname: Thalmann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002119:Calcium Carbonate / Q000737:chemistry* / Q000378:metabolism; D002135:Calcium-Binding Proteins; D002460:Cell Line; D002942:Circular Dichroism; D003460:Crystallization; D016326:Extracellular Matrix Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008027:Light; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010037:Otolithic Membrane / Q000737:chemistry / Q000378:metabolism; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D012542:Scattering, Radiation; D013059:Spectrum Analysis, Raman; D040681:Structural Homology, Protein; D013329:Structure-Activity Relationship; D014162:Transfection
chemical_list: D002135:Calcium-Binding Proteins; D016326:Extracellular Matrix Proteins; C512837:Oc90 protein, mouse; D011994:Recombinant Proteins; D002119:Calcium Carbonate