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Mutational Analysis Of Parkin Gene And Its Association Eith Parkinson'S Disease

By: Misbah Hussain | Prof. Dr. Masroor Ellahi Babar.
Contributor(s): Miss. Asma | Miss. Saeeda Kalsoom.
Material type: materialTypeLabelBookPublisher: 2013Subject(s): Institute of Biochemistry & BiotechnologyDDC classification: 1643,T Dissertation note: Parkinson's disease (PD) is a neurodegenerative disease in which dopamine neurons are lost in sabstantia nigra. It is second most prevalent disorder after Alzheimer's disease. PD is also referred as movement disorder because its main characteristics are movement related like rigidity, slowness of movement and resting tremors which are caused by the loss of dopamine in putamen specially its caudal portion Lots of work has been done on PD but still actual mechanism of its progression is unknown. Scientists have declared genetic mutations, oxidative stress, pesticide exposure, high caloric food etc as causative agents for PD. There are 6 genes which are responsible for PD. Mutations in the parkin gene produce Early Onset Parkinson's disease (EOPD) in 50-60% of patients. parkin gene encodes for Parkin protein which consist of 4 domains (UBL, RING1, IBR, RING2). UBL domain is involved in the interaction with substrates. While the other 3 domains helps in interaction with E2 Ubiquitin- conjugating enzyme. Most frequent mutations in this gene are the point mutations. 2nd exon of parkin gene is considered as one of the hotspot for mutations. First three exons code for Ubiquitin-like (UBL) domain, which help in the attachment with substrates like Rpn10 subunit of 26S proteasome. Rpn10 subunit of 26S proteasome binds with Arginine at position 42 located in UBL domain of parkin. This 26S proteasome degrade the unfolded proteins into short peptides of 7-8 amino acids in length, which are then further degraded in shorter fragments which are then used in the formation of new proteins. In current study, I have done mutational analysis of parkin gene and found one very important noval point mutation which is a transition C'T mutation in UBL domain, which results in the amino acid substitution Arginine' Cysteine at position 42 (location where Rpn10 subunit of 26S proteasome binds). Arginine and Cysteine are biochemically different in nature and in the classification based on R group they belongs to different groups. Arginine is a polar positive amino acid while Cysteine is polar uncharged and contain sulfur molecule. So, this amino acid change could result in the decreased or no attachment of 26S proteasome (catalyzes protein degradation) via its Rpn10 subunit which selectively binds with the poly-ubiquitin chain of damaged proteins. So, this decreased attachment inhibits the degradation of misfolded and defected protein in the cytosol. In result of this inhibition these defected proteins will start gathering and form aggregates within the cytosol of cell it will eventually decrease cell's function and cell will start dying.
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Parkinson's disease (PD) is a neurodegenerative disease in which dopamine neurons are lost in sabstantia nigra. It is second most prevalent disorder after Alzheimer's disease. PD is also referred as movement disorder because its main characteristics are movement related like rigidity, slowness of movement and resting tremors which are caused by the loss of dopamine in putamen specially its caudal portion
Lots of work has been done on PD but still actual mechanism of its progression is unknown. Scientists have declared genetic mutations, oxidative stress, pesticide exposure, high caloric food etc as causative agents for PD. There are 6 genes which are responsible for PD. Mutations in the parkin gene produce Early Onset Parkinson's disease (EOPD) in 50-60% of patients. parkin gene encodes for Parkin protein which consist of 4 domains (UBL, RING1, IBR, RING2). UBL domain is involved in the interaction with substrates. While the other 3 domains helps in interaction with E2 Ubiquitin- conjugating enzyme.
Most frequent mutations in this gene are the point mutations. 2nd exon of parkin gene is considered as one of the hotspot for mutations. First three exons code for Ubiquitin-like (UBL) domain, which help in the attachment with substrates like Rpn10 subunit of 26S proteasome. Rpn10 subunit of 26S proteasome binds with Arginine at position 42 located in UBL domain of parkin. This 26S proteasome degrade the unfolded proteins into short peptides of 7-8 amino acids in length, which are then further degraded in shorter fragments which are then used in the formation of new proteins.
In current study, I have done mutational analysis of parkin gene and found one very important noval point mutation which is a transition C'T mutation in UBL domain, which results in the amino acid substitution Arginine' Cysteine at position 42 (location where Rpn10 subunit of 26S proteasome binds). Arginine and Cysteine are biochemically different in nature and in the classification based on R group they belongs to different groups. Arginine is a polar positive amino acid while Cysteine is polar uncharged and contain sulfur molecule. So, this amino acid change could result in the decreased or no attachment of 26S proteasome (catalyzes protein degradation) via its Rpn10 subunit which selectively binds with the poly-ubiquitin chain of damaged proteins.
So, this decreased attachment inhibits the degradation of misfolded and defected protein in the cytosol. In result of this inhibition these defected proteins will start gathering and form aggregates within the cytosol of cell it will eventually decrease cell's function and cell will start dying.

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