OCP2 exists as a dimer in the organ of Corti

OCP2 is one of the most abundant proteins in the organ of Corti (OC), comprising approximately 5% of the total protein in the supporting cell population. Although the very close homolog, Skp1p, has been implicated in regulating cell-cycle progression, the function of OCP2 in the terminally differentiated cochlea is presently unknown. We have purified recombinant OCP2 from Escherichia coli and examined the protein by analytical ultracentrifugation. Interestingly, sedimentation equilibrium data collected at 20 degrees C unequivocally indicate that, at the concentrations present in the OC, free OCP2 would exist as a dimeric species. The apparent sedimentation coefficient is independent of concentration at loading concentrations between 10 and 100 microM, indicating the absence of a significant monomer-dimer equilibrium in this concentration range. The functional significance of this finding is discussed.