RESUMO
OBJECTIVE: Mutations in the gap junction protein beta-2 gene ('GJB2') are known to be responsible for mild to profound congenital and late-onset hearing loss. This study aimed to investigate the molecular basis of progressive hearing loss compared with non-progressive hearing loss. METHODS: Following clinical otorhinolaryngological evaluation, a genetic analysis was performed in a cohort of 72 patients with progressive sensorineural hearing loss. RESULTS: Pathological genotypes were established in 16 patients (22.2 per cent). Six different gap junction protein beta-2 gene mutations were detected in 15 patients, with the c.35delG mutation responsible for 56 per cent of the mutated alleles. A novel gap junction protein beta-6 gene ('GJB6') mutation (p.Met203Val) was observed in one patient with mild progressive hearing loss. CONCLUSION: Analyses of gap junction protein beta-2 and -6 genes revealed that similar pathological genotypes, occurring with similar frequencies, were responsible for progressive hearing loss, compared with reported genotypes for non-progressive hearing loss patients. Thus, genotype cannot be used to differentiate non-progressive from progressive hearing loss cases; in this study, patients both with and without an established pathological genotype had a similar clinical course.
Assuntos
Conexinas/genética , Perda Auditiva Neurossensorial/genética , Mutação , Adolescente , Adulto , Alelos , Estudos de Casos e Controles , Criança , Pré-Escolar , Estudos de Coortes , Conexina 26 , Conexina 30 , Feminino , Genótipo , Humanos , Lactente , Masculino , Pessoa de Meia-IdadeRESUMO
Lapstatin, a low-molecular-weight aminopeptidase inhibitor, was purified to homogeneity from Streptomyces rimosus culture filtrates. The purification procedure included extraction with methanol, followed by chromatography on Dowex 50WX4, AG50WX4, and HPLC RP C18 columns. By amino acid analysis, mass spectrometry, and NMR spectroscopy, the structure of lapstatin was shown to be 3-amino-2-hydroxy-4-methylpentanoylvaline. Lapstatin inhibited the extracellular leucine aminopeptidases from Streptomyces rimosus, Streptomyces griseus, and Aeromonas proteolytica with an IC50 in the range of 0.3-2.4 microM. IC50 values for other enzymes tested were at least tenfold higher. Leucine aminopeptidase from Streptomyces griseus was inhibited in a competitive manner, with an inhibition constant of 5 x 10(-7) M. Lapstatin is the first low-molecular-weight compound isolated from streptomycetes shown to inhibit an autogenous aminopeptidase.