title: Effect of Otoconial Proteins Fetuin A, Osteopontin, and Otoconin 90 on the Nucleation and Growth of Calcite.
abstract: We investigated the roles of three proteins associated with the formation of otoconia including fetuin A, osteopontin (OPN), and otoconin 90 (OC90). In situ atomic force microscopy (AFM) studies of the effects of these proteins on the growth of atomic steps on calcite surfaces were performed to obtain insight into their effects on the growth kinetics. We also used scanning electron microscopy to examine the effects of these proteins on crystal morphology. All three proteins were found to be potent inhibitors of calcite growth, although fetuin A promoted growth at concentrations below about 40 nM and only became an inhibitor at higher concentrations. We then used in situ optical microscopy to observe calcite nucleation on films of these proteins adsorbed onto mica surfaces. By measuring the calcite nucleation rate as a function of supersaturation, the value of the interfacial energy that controls the free energy barrier to heterogeneous nucleation was determined for each protein. OPN and OC90 films led to significantly reduced interfacial energies as compared to the value for homogeneous calcite nucleation in bulk solution. The value for fetuin A was equal to that for bulk solution within experimental error. Zeta potential measurements showed all of the proteins possessed negative surface charge and varied in magnitude according to sequence fetuin A > OC90 > OPN. In addition, the interfacial energies exhibited an inverse scaling with the zeta potential. In analogy to previous measurements on polysaccharide films, this scaling indicates the differences between the proteins arise from the effect of protein surface charge on the solution-substrate interfacial energy.
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States ; Department of Chemistry, The George Washington University , Washington, D.C. 20052, United States ; The Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Mina
authors.initials: M
authors.lastname: Hong
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Washington University in St. Louis , St. Louis, Missouri 63110, United States.
authors.forename: K Trent
authors.initials: KT
authors.lastname: Moreland
authors.affiliation: The Molecular Foundry, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Jiajun
authors.initials: J
authors.lastname: Chen
authors.affiliation: Department of Chemistry, The George Washington University , Washington, D.C. 20052, United States.
authors.forename: Henry H
authors.initials: HH
authors.lastname: Teng
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, Washington University in St. Louis , St. Louis, Missouri 63110, United States.
authors.forename: Ruediger
authors.initials: R
authors.lastname: Thalmann
authors.affiliation: Physical Sciences Division, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: James J
authors.initials: JJ
authors.lastname: De Yoreo