Proteomic Analysis of the Vertigo and Deafness gene, COCH

Abstract

In recent years, due to the technological advances of molecular biology, many important findings are reported in the field of hereditary hearing impairment (HHI). Some of the HHI genes have been cloned and the mutations of those genes were identified. Much knowledge has accumulated about the HHI genes, however, little research has been done regarding the protein products of those genes.Two-dimensional gel electrophoresis and direct protein sequencing, together with searches in protein and DNA, EST databases, have accelerated the protein-identification process. The proteome is the expressed protein complement of a genome and proteomics is functional genomics at the protein level. To characterize deafness genes at the protein level as well as other inner ear proteins, we have performed a proteomic analysis of the inner ear proteins.In the process of analysis, we have found very unique properties of the protein product of a deafness gene, LOCH. The LOCH gene is responsible for one of the HHI, DFNA9. DFNA9 is the locus in humans reported to involve vestibular problems as part of the non-syndromic deafness phenotype. The primary pathologic change of the DFNA9 is a deposit of acid polymucosaccharide ground substance is the cribrose areas; in the spiral ligament, limbus, and spiral lamina of the cochlea; and in the stroma of the maculae and cristae. The end result is neuronal degeneration in association with varying degrees of atrophic change in the sense organs. Recently, it is suggested that missense mutation in the LOCH gene might be related to the pathogenesis of Meniere's disease.Our results show that the protein product of the Coch gene constitutes 70% of inner ear proteins and is composed of 16 different protein spots with charge and size heterogeneity. Amino acid analysis of these spots identified 3 groups of isoforms of Coch protein (Cochlin), p63s, p44s and p40s. All 6 mutations found in DFNA9 patients are found in p63s, not in p44s and p40s.Heterogeneity of this protein suggests that the Coch gene is processed in several ways and may suggest that the Coch protein is very important in the inner ear function. Study of the Coch protein might provide more information on the mechanism of hearing and vestibular disorders.