Functional analysis of novel gene products, citrin and aralar

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A novel gene, SLC25A13, was identified by homozygosity mapping and positional cloning as the responsible for adult-onset type II citrullinemia (CTLN2). The overall structure of citrin is very similar to that of aralar, encoded by the gene SLC25A12. In this project we have studied the function of citrin and aralar for use in elucidation of crisis mechanism, diagnosis and treatment of CTLN2.Citrin was distributed mainly in the liver, kidney, heart and newborn small intestine. Aralar was expressed in diaphragm, skeletal muscle, heart, brain, and kidney, but not in the liver. It is important for the liver-specific disorder of citrin deficiency, CTLN2, to note that the liver is the only organ expressing citrin in large amounts, but that it dose not express aralar. Citrin and aralar localized to mitochondrial inner membrane were found to be isoforms of mitochondrial aspartate glutamate carriers (AGC) with active AGC activity in their C-half domains and EF-hand Ca binding in their N-terminal … More dpmains. The AGC is an essential component of malate aspartate (NADH) shuttle. The main function of the shuttle is the transport of NADH )reducing equivalent) from cytosol to mitochondria. The AGC is also important for urea synthesis from ammonia, because aspartate formed from ammonia via glutamate in the mitochondria should go out to cytosol through AGC and be supplied for argininosuccinate synthetase. These result suggest that either or both of these effects could lead to the symptoms of CTLN2.In order to identify the protein that interact with citrin, we screened cDNA library derived from human liver by using yeast two hybrid system. After sequencing analysis, we have identified two proteins, one is a protein which regulats Ca effect of protein kinase C, and the other is a redox related protein. The precise characterization of interaction between citrin and these protein needs to be assessed. Expression of mutated citrin and GFP fusion proteins, in which most oftransmembrane domain is retained, showed a punctuate pattern of distribution that colocalized with mitochondria selective dye, MitoTracker Red CMXRos. Further study is required to determine whether this mitochondrial punctuation induces cell death process, apoptosis. Less