Leucine-rich repeat kinase 2 (LRRK2), also known as dardarin (from the Basque word "dardara" which means trembling) and PARK8 (from early identified association with Parkinson's disease), is a large, multifunctional kinase enzyme that in humans is encoded by the LRRK2 gene. [5] [6] LRRK2 is a member of the leucine-rich repeat kinase family. Variants of this gene are associated with an increased risk of Parkinson's disease and Crohn's disease. [5] [6]
The LRRK2 gene encodes a protein with an armadillo repeats (ARM) region, an ankyrin repeat (ANK) region, a leucine-rich repeat (LRR) domain, a kinase domain, a RAS domain, a GTPase domain, and a WD40 domain. The protein is present largely in the cytoplasm but also associates with the mitochondrial outer membrane.
LRRK2 interacts with the C-terminal R2 RING finger domain of parkin, and parkin interacted with the COR domain of LRRK2. Expression of mutant LRRK2 induced apoptotic cell death in neuroblastoma cells and in mouse cortical neurons. [7]
Expression of LRRK2 mutants implicated in autosomal dominant Parkinson's disease causes shortening and simplification of the dendritic tree in vivo and in cultured neurons. [8] This is mediated in part by alterations in macroautophagy, [9] [10] [11] [12] [13] and can be prevented by protein kinase A regulation of the autophagy protein LC3. [14] The G2019S and R1441C mutations elicit post-synaptic calcium imbalance, leading to excess mitochondrial clearance from dendrites by mitophagy. [15] LRRK2 is also a substrate for chaperone-mediated autophagy. [16]
Mutations in this gene have been associated with Parkinson's disease type 8. [17] [18]
The Gly2019Ser mutation results in enhanced kinase activity, and is a relatively common cause of familial Parkinson's disease in Caucasians. [19] It may also cause sporadic Parkinson's disease. The mutated Gly amino acid is conserved in all kinase domains of all species.
The Gly2019Ser mutation is one of a small number of LRRK2 mutations proven to cause Parkinson's disease. Of these, Gly2019Ser is the most common in the Western World, accounting for ~2% of all Parkinson's disease cases in North American Caucasians. This mutation is enriched in certain populations, being found in approximately 20% of all Ashkenazi Jewish Parkinson's disease patients and in approximately 40% of all Parkinson's disease patients of North African Berber Arab ancestry. [20] [21]
Unexpectedly, genomewide association studies have found an association between LRRK2 and Crohn's disease as well as with Parkinson's disease, suggesting that the two diseases share common pathways. [22] [23]
Attempts have been made to grow crystals of the LRRK2 aboard the International Space Station, as the low-gravity environment renders the protein less susceptible to sedimentation and convection, and thus more crystallizable. [24]
Mutations in the LRRK2 gene is the main factor in contributing to the genetic development of Parkinson's disease, and over 100 mutations in this gene have been shown to increase the chance of PD development. These mutations are most commonly seen in North African Arab Berber, Chinese, and Japanese populations. [25]
Alpha-synuclein(aSyn) is a protein that, in humans, is encoded by the SNCA gene. Alpha-synuclein is a neuronal protein that regulates synaptic vesicle trafficking and subsequent neurotransmitter release.
Autophagy is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism. It allows the orderly degradation and recycling of cellular components. Although initially characterized as a primordial degradation pathway induced to protect against starvation, it has become increasingly clear that autophagy also plays a major role in the homeostasis of non-starved cells. Defects in autophagy have been linked to various human diseases, including neurodegeneration and cancer, and interest in modulating autophagy as a potential treatment for these diseases has grown rapidly.
CREB-TF is a cellular transcription factor. It binds to certain DNA sequences called cAMP response elements (CRE), thereby increasing or decreasing the transcription of the genes. CREB was first described in 1987 as a cAMP-responsive transcription factor regulating the somatostatin gene.
Ubiquitin carboxy-terminal hydrolase L1 is a deubiquitinating enzyme.
Parkin is a 465-amino acid residue E3 ubiquitin ligase, a protein that in humans and mice is encoded by the PARK2 gene. Parkin plays a critical role in ubiquitination – the process whereby molecules are covalently labelled with ubiquitin (Ub) and directed towards degradation in proteasomes or lysosomes. Ubiquitination involves the sequential action of three enzymes. First, an E1 ubiquitin-activating enzyme binds to inactive Ub in eukaryotic cells via a thioester bond and mobilises it in an ATP-dependent process. Ub is then transferred to an E2 ubiquitin-conjugating enzyme before being conjugated to the target protein via an E3 ubiquitin ligase. There exists a multitude of E3 ligases, which differ in structure and substrate specificity to allow selective targeting of proteins to intracellular degradation.
A neurodegenerative disease is caused by the progressive loss of structure or function of neurons, in the process known as neurodegeneration. Such neuronal damage may ultimately involve cell death. Neurodegenerative diseases include amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, multiple system atrophy, tauopathies, and prion diseases. Neurodegeneration can be found in the brain at many different levels of neuronal circuitry, ranging from molecular to systemic. Because there is no known way to reverse the progressive degeneration of neurons, these diseases are considered to be incurable; however research has shown that the two major contributing factors to neurodegeneration are oxidative stress and inflammation. Biomedical research has revealed many similarities between these diseases at the subcellular level, including atypical protein assemblies and induced cell death. These similarities suggest that therapeutic advances against one neurodegenerative disease might ameliorate other diseases as well.
Glial cell line-derived neurotrophic factor (GDNF) is a protein that, in humans, is encoded by the GDNF gene. GDNF is a small protein that potently promotes the survival of many types of neurons. It signals through GFRα receptors, particularly GFRα1. It is also responsible for the determination of spermatogonia into primary spermatocytes, i.e. it is received by RET proto-oncogene (RET) and by forming gradient with SCF it divides the spermatogonia into two cells. As the result there is retention of spermatogonia and formation of spermatocyte.
Protein deglycase DJ-1, also known as Parkinson disease protein 7, is a protein which in humans is encoded by the PARK7 gene.
PTEN-induced kinase 1 (PINK1) is a mitochondrial serine/threonine-protein kinase encoded by the PINK1 gene.
Kalirin, also known as Huntingtin-associated protein-interacting protein (HAPIP), protein duo (DUO), or serine/threonine-protein kinase with Dbl- and pleckstrin homology domain, is a protein that in humans is encoded by the KALRN gene. Kalirin was first identified in 1997 as a protein interacting with huntingtin-associated protein 1. Is also known to play an important role in nerve growth and axonal development.
Autophagy related 5 (ATG5) is a protein that, in humans, is encoded by the ATG5 gene located on Chromosome 6. It is an E3 ubi autophagic cell death. ATG5 is a key protein involved in the extension of the phagophoric membrane in autophagic vesicles. It is activated by ATG7 and forms a complex with ATG12 and ATG16L1. This complex is necessary for LC3-I conjugation to PE (phosphatidylethanolamine) to form LC3-II. ATG5 can also act as a pro-apoptotic molecule targeted to the mitochondria. Under low levels of DNA damage, ATG5 can translocate to the nucleus and interact with survivin.
Vacuolar protein sorting ortholog 35 (VPS35) is a protein involved in autophagy and is implicated in neurodegenerative diseases, such as Parkinson's disease (PD) and Alzheimer's disease (AD). VPS35 is part of a complex called the retromer, which is responsible for transporting select cargo proteins between vesicular structures and the Golgi apparatus. Mutations in the VPS35 gene (VPS35) cause aberrant autophagy, where cargo proteins fail to be transported and dysfunctional or unnecessary proteins fail to be degraded. There are numerous pathways affected by altered VPS35 levels and activity, which have clinical significance in neurodegeneration. There is therapeutic relevance for VPS35, as interventions aimed at correcting VPS35 function are in speculation.
Leucine-rich repeat serine/threonine-protein kinase 1 is an enzyme that in humans is encoded by the LRRK1 gene.
Leucine rich repeat and Immunoglobin-like domain-containing protein 1 also known as LINGO-1 is a protein which is encoded by the LINGO1 gene in humans. It belongs to the family of leucine-rich repeat proteins which are known for playing key roles in the biology of the central nervous system. LINGO-1 is a functional component of the Nogo receptor also known as the reticulon 4 receptor.
Parkinson's disease (PD) is a degenerative disorder of the central nervous system. Most people with PD have idiopathic Parkinson's disease. A small proportion of cases, however, can be attributed to known genetic factors. Other factors such as environmental toxins, herbicides, pesticides, and fungicides, have been associated with the risk of developing PD, but no causal relationships have been proven.
Phosphomimetics are amino acid substitutions that mimic a phosphorylated protein, thereby activating the protein. Within cells, proteins are commonly modified at serine, tyrosine and threonine amino acids by adding a phosphate group. Phosphorylation is a common mode of activating or deactivating a protein as a form of regulation. However some non-phosphorylated amino acids appear chemically similar to phosphorylated amino acids. Therefore, by replacing an amino acid, the protein may maintain a higher level of activity. For example, aspartic acid is chemically similar to phospho-serine. Therefore, when an aspartic acid replaces a serine, it is a phosphomimetic of phospho-serine and can make the protein always in its phosphorylated form. Phosphonate-based compounds have been used as phosphotyrosine analogues, as they are less enzyme labile and are physiologically more stable.
Leucine rich repeat and Ig domain containing 2 is a protein that in humans is encoded by the LINGO2 gene.
Ted M. Dawson is an American neurologist and neuroscientist. He is the Leonard and Madlyn Abramson Professor in Neurodegenerative Diseases and Director of the Institute for Cell Engineering at Johns Hopkins University School of Medicine. He has joint appointments in the Department of Neurology, Neuroscience and Department of Pharmacology and Molecular Sciences.
Valina L. Dawson is an American neuroscientist who is the director of the Programs in Neuroregeneration and Stem Cells at the Institute for Cell Engineering at the Johns Hopkins University School of Medicine. She has joint appointments in the Department of Neurology, Neuroscience and Physiology. She is a member of the Graduate Program in Cellular and Molecular Medicine and Biochemistry, Cellular and Molecular Biology.
Animal models of Parkinson's disease are essential in the research field and widely used to study Parkinson's disease. Parkinson's disease is a neurodegenerative disorder, characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). The loss of the dopamine neurons in the brain, results in motor dysfunction, ultimately causing the four cardinal symptoms of PD: tremor, rigidity, postural instability, and bradykinesia. It is the second most prevalent neurodegenerative disease, following Alzheimer's disease. It is estimated that nearly one million people could be living with PD in the United States.
A collaboration between the Michael J. Fox Foundation, of New York City, and Merck Research Laboratories, of Kenilworth, New Jersey, will seek to grow crystals of a key gene protein, Leucine-Rich Repeat Kinase 2 (LRRK2), in an effort to advance the search for a cure for Parkinson's disease. Crystals cultured in the absence of gravity are less susceptible to sedimentation and convection, rendering them larger and easier to map than those grown in labs on Earth in order to design medicines.
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