Raabia Bibi (2012-VA-537)

DNA Based Characterization Of Arginase Gene From Geobacillus Sp. SBS-4s - 2015. - 102p.;

Geobacillus is a group gram-positive, rod-shaped, aerobic, endospore-forming and obligate thermophilic bacteria, isolated from the diverse habitats, hot springs, thermal environments, terrestrial soils, deep sea sediments (Zeigler, 2014), petroleum and soil of desserts (Claus and Berkeley 1986). It grows at a wide range of temperature from 45 to 75°C and pH ranging from 6.2 to 7.8 (Nazina et al. 2001). These bacteria survives at higher temperature where most of other living species fail to survive (Claus and Berkeley 1986). Geobacillus have achieved a significant population with a worldwide distribution, probably in large part due to adaptive features of their spores (Zeigler, 2014). These can be found singly or in short chains and motile by means of peritrichous flagella and is capable of secreting a wide variety of extracellular and intracellular enzymes i.e amylase, lipase, carboxypeptidase, cellulase, xylanase, protease and galactosidase (Fogarth et al. 1974; Obeidat et al. 2012).
Geobacillus sp. SBS-4S was isolated from hot spring located in Gilgit, Northern areas of Pakistan. It was found to be an aerobic, gram-positive and rod-shaped bacteria having ability to hydrolyze a variety of sugars, carboxylic acids and hydrocarbons at elevated temperatures from 45 to 75°C. SBS-4S was found to be involved in the production of various intra and extra cellular enzymes (Tayyab et al. 2011).
Arginase is the enzyme responsible for the degradation of arginine resulting in the production of urea and ornithine (Kaur et al. 2009). It is accomplished by the cleaving of the guanidinium group from arginine which yields urea (Turras et al. 2008). Arginase present in many mammals (Homo sapiens), Bacilli (cyanobacteria), protozoa (Entamoeba histolytica), yeast (Saccharomyces cerevisiae), fungi (Neurospora crassa) and plants (Lathyrus sativus) etc (Kaur et al. 2009). The crystal structure of arginases have been determined by X ray crystallographic studies. This is a manganese dependent enzyme. The enzyme shows its activity through the metal ion. Metal ion is actively responsible for the incorporation of water molecules essential for the activity of the enzyme. A second proposed mechanism, based on electron paramagnetic resonance (EPR) studies postulates direct coordination of the substrate to manganese and disruption of the aqua bridge. Arginases are homo-oligomers, with a typical subunit mass of 32 to 36 kDa (Bewley et al. 1999).
There are two types of arginases, arginase-I and arginase-II, located in the cytoplasm and mitochondria, respectively. The principal ureagenic enzyme activity arginase-I is most abundant in normal mammalian liver and acts in coordination with the other enzymes of the urea cycle to sequester and eliminate excess nitrogen from the body. The second form arginase-II can be found in many organs, with the highest levels found in kidney and prostate where as lower levels in macrophages and lactating mammary glands (Iyer et al. 2002).
Important role of arginase in controlling the cellular levels of arginine and ornithine, which are required for various critical metabolic processes, including protein synthesis and the production of creatine, polyamines, proline and nitric oxide (NO). Type II arginase is found in a variety of different tissues and have a key role in the regulation of urea cycle arginine metabolism by regulating levels of arginine in the cell (Bewley et al. 1999). The enzyme arginase plays key role in the pathogenesis of pulmonary disorders such as asthma through dysregulation of L-arginine metabolism and modulation of nitric oxide (NO) homeostasis and it also play role in the development of chronic airway remodeling through formation of ornithine with downstream production of polyamines and L-proline, which are involved in processes of cellular proliferation and collagen deposition (Benson et al. 2011). Arginase involved in tissue repair processes by the synthesis of L-ornithine, which is the precursor of polyamines and proline that are involved in cell proliferation and collagen synthesis (Maarsingh et al. 2009).
Genetically engineered arginase as fusion protein with prolonged half-life and increased efficacy are used to treat different tumor lines that inhibit cell proliferation and impaired cellular migration in vitro and in vivo (Li et al. 2013). This is a arginine-degrading and ornithine producing enzyme and is used to treat arginine-dependent cancers (Yu et al. 2013). Chemically modified arginase-II has been employed for the treatment of taper liver tumor and L5178Y murine leukemia (Kaur et al. 2009). The enzyme was cloned and expressed in E. coli and subsequently conjugated to polyethylene glycol to increase the circulating half-life and decrease the immunogenicity of the recombinant mycoplasma enzyme. The human hepatocellular carcinoma, melanoma cell lines and tissue samples do not express argininosuccinate synthetase (ASS), making them auxotrophic for arginine and thus reasonable candidates for arginine deprivation (Yang et al. 2010).
Arginase is induced in murine myeloid cells mainly by T-helper 2 cells cytokines and inflammatory agents and participates in a variety of inflammatory diseases by down-regulation of nitric oxide synthesis, induction of fibrosis and tissue regeneration. In humans, arginase I is constitutively expressed in polymorphonuclear neutrophils and is liberated during inflammation. Myeloid cell arginase-mediated L-arginine depletion profoundly suppresses T cell immune responses and this is a fundamental mechanism of inflammation-associated immunosuppression. Pharmacological interference with L-arginine metabolism is a novel promising strategy in the treatment of cancer, autoimmunity or unwanted immune deviation (Munder, 2009).
Arginase has very important role in nitrogen fixation and fruit ripening (Yu et al. 2013). Putrescine (1,4-butanediamine) is the product obtained from arginine with the highest market value and it is used as an intermediate in a large number of industries, including the pharmaceutical industry, agrochemical industry and textile industry (Turras et al. 2008).
Arginine is a semi-essential amino acid and is the precursor for the formation of nitric oxide (NO) by nitric oxide synthases (Getz and Reardon, 2006). One of the major functions of arginine within the body is as an intermediate in the urea cycle. In the cytosol of hepatocytes, arginase-I removes the guanidine group from arginine to produce urea and ornithine. Urea is then transported from the hepatocyte into the bloodstream and ornithine is used to regenerate arginine within the hepatocyte. Arginine deficiency causes several disorder like, hyper cholesterolemia, hypertension, diabetes mellitus, kidney failure, hyper homo-cysteinemia, smoking, and aging (Alvares et al. 2012). Arginine is used to modulate the cellular immune response during infection. The generation of nitric oxide from arginine is responsible for efficient immune response (Das et al. 2010).
Arginine is synthesised in humans and other mammals from citrulline in two steps through the urea cycle enzymes, argininosuccinate synthetase (ASS) and argininosuccinate lyase (ASL). ASS catalyses the conversion of citrulline and aspartic acid to argininosuccinate, which is then converted to arginine and fumaric acid by ASL (Yang et al. 2010).
Ararinase play important role in conversion of arginine to 1,4–butanediamine (a building block for nylon-4,6), through two main transformations: the hydrolysis of arginine to ornithine and urea; and the decarboxylation of ornithine to 1,4–butanediamine and carbon dioxide. Both steps can be catalyzed chemically or enzymatically (Turras et al. 2008).
The present study deals with the characterization of arginase gene.

Institute of Biochemistry and Biotechnology (IBBT)


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