Glucose transporters are integral membrane proteins that mediate the transport of glucose and structurally related substances across cellular membranes. The role of the sodium-glucose cotransporters is to not only absorb glucose, but to also absorb sodium and to then reabsorb the sodium and glucose from the tubule of the nephron. Two families of glucose transporter have been identified: the facilitated diffusion glucose transporter family (GLUT family), also known as 'uniporters,' and the sodium-dependent glucose transporter family (SGLT family), also known as 'cotransporters' or 'symporters. The SLC5A1 gene encodes a protein that is involved in the active transport of glucose and galactose into eukaryotic and some prokaryotic cells.
Co-transport proteins of mammalian cell membranes had eluded efforts of purification with classical biochemical methods until the late 1980s. These proteins had proven difficult to isolate because they contain hydrophilic and hydrophobic sequences and exist in membranes only in very low abundance (<0.2% of membrane proteins). The rabbit form of SGLT1 was the first mammalian co-transport protein ever to be cloned and sequenced, and this was reported in 1987. To circumvent the difficulties with traditional isolation methods, a novel expression cloning technique was used. Size-fractionation of large amounts of rabbit intestinal mRNA with preparative gel electrophoresis were then sequentially injected into Xenopus oocytes to ultimately find the RNA species that induced the expression of sodium-glucose cotransport.
SLC5A1 is important because of its role in the absorption of glucose and sodium, however, mutations in the gene can cause serious effects. A mutation in the SLC5A1 gene can cause problems creating the SGLT1 protein, leading to a rare glucose-galactose malabsorption disease. Glucose-galactose malabsorption occurs when the lining of the intestinal cells can't take in glucose and galactose which prevents the use of those molecules in catabolism and anabolism. The disease has symptoms that consist of watery and/or acidic diarrhea which is the result of water retention in the intestinal lumen and osmotic loss created by non-absorbed glucose, galactose and sodium. Glucose-Galactose malabsorption can cause death, due to loss of water from diarrhea, if the disease isn't treated soon. To counteract the disease, oral rehydration therapy is performed using sodium, glucose, and water for intestinal reabsorption.
The SLC5A1 cotransporter is mainly expressed in the lumen of the small intestine, kidney, parotid glands, submandibular glands and in the heart.
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