Calcium-binding proteins in organ of Corti and basilar papilla: CBP-15, an unidentified calcium-binding protein of the inner ear.
In a previous paper (Thalmann et al., 1993) we reported that the amino acid sequence of OCP2, a low molecular weight acidic protein present in extremely high concentrations in the organ of Corti and absent in the basilar papilla, exhibits a rudimentary EF-hand--a potential calcium-binding domain. The present study was undertaken to determine whether OCP2 binds 45-calcium under non-denaturing conditions following separation by isoelectric focusing and transblotting. The same criterion was used to determine whether the EF-hands of several other calcium-binding proteins (CBP) are functional in organ of Corti and basilar papilla. OCP2 exhibited no 45-calcium binding. Calmodulin, present in the organ of Corti in extremely high concentrations and lower in basilar papilla, showed strong 45-calcium binding in both structures. While calbindin represents a major protein in basilar papilla and binds 45-calcium, this protein is a minor component in the organ of Corti; whether it binds 45-calcium remains to be decided. By extending the pI range in the acidic region of isoelectric focusing, a 15 kDa, highly acidic (pI approximately 3.1) protein was revealed that constitutes a major protein in the organ of Corti; the protein was not detectable in the basilar papilla, spiral ligament/stria vascularis complex and numerous other organs tested. It remains to be resolved whether this protein represents an isoform of parvalbumin or a novel CBP. The differential make-up of CBPs between the mammalian organ of Corti and the avian basilar papilla is discussed.
Senarita
M
M
Department of Otolaryngology, Washington University, St. Louis MO 63110, USA.
Thalmann
I
I
Shibasaki
O
O
Thalmann
R
R
D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D064026:Calbindins; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D006168:Guinea Pigs; D007525:Isoelectric Focusing; D008970:Molecular Weight; D009925:Organ of Corti / Q000378:metabolism*; D011489:Protein Denaturation; D044786:S-Phase Kinase-Associated Proteins; D064030:S100 Calcium Binding Protein G / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
D064026:Calbindins; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D044786:S-Phase Kinase-Associated Proteins; D064030:S100 Calcium Binding Protein G; C097351:SKP1 protein, human; D014157:Transcription Factors