GTP環化水解酵素突變與新發現的調節因子之生化特性調控
Biochemical Regulation of Mutant GTP Cyclohydrolase I and Novel Regulators
Date Issued
2007
Date
2007
Author(s)
Chiou, Yu-Wei
DOI
zh-TW
Abstract
Dopa-responsive dystonia (DRD) is induced by a deficiency of GTP cyclohydrolase I (GCH) and has a postulated autosomal dominant inheritance with a low penetrance. GCH is a key enzyme for biosynthesis of BH4, a cofactor of several monooxygenases. The first part we found an autosomal recessive GCH mutant R24RS possess normal activity in both in vitro and in vivo. It has been proposed the disease may be due to lower mutant protein expression level regulated in a posttranscriptional way. To investigate the mechanism of dominant negative (DN) effect in DRD, we analyzed the biochemical property of two GCH mutants G201E and L79P examined in a cell model. The GCH mutant is unstable and is degraded through lysosomal proteolysis using inhibitor analysis and pulse chase experiment (Part II). Further we found overexpressed G201E was mainly localized in LAMP-1-positive lysosomes and EEA1 early endososomes compartment (Part III). In part IV, a novel protein BEC1 enriched in non-DN cell identified through cDNA subtraction was investigated. We analyzed the distribution of BEC1 and showed that BEC1 protein was prominently expressed in neuronal cells including striatum, cortex and some of the Purkinje cells in cerebellum. The function of BEC1 was still unknown, but it could promote wild-type GCH expression and reduce insoluble mutant protein in lysosomes. We suspect that BEC1 could activate a surveillance mechanism for the insoluble proteins. In Part V, we identified that overexpression of small heat shock protein Hsp27 may accelerate degradation mutant GCH proteins. The role of Hsp27 is discussed.
Subjects
肌肉張力不全症
GTP環化水解酶
BEC1
Hsp27
顯性負面調控
溶酶
體
DRD
GCH
dominant negative
lysosome
Type
other
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