Glucose and other hexoses transporters in marine invertebrates: A mini review

Abstract

Glucose and related hexoses are very important metabolic substrates. Their most important function is to provide quick fuel for most organisms in all three kingdoms because they are the first substrate for energy production in the form of ATP through glycolysis and the subsequent metabolic pathways. In this paper we review the current information about how glucose and related hexoses are transported across biological membranes to carry out their function either as a metabolic molecule or as energy store in marine invertebrate organisms. In these animals, there are two sugar transport systems that are mediated by the sodium/solute symporter family proteins (SGLT) and the major facilitative super-family proteins (GLUT). The most studied sugar transporters in marine invertebrates are involved with dietary sugar uptake, such as SGLT1, SGLT4, GLUT2 and GLUT5, however more studies need to be done to extend the knowledge about these and other sugar transporters involved in metabolic processes. Transporters of glucose and other hexosesGlucose is the major product of carbon fixation by photosynthetic organisms and consequently, it is the most abundant molecule on earth. Glucose is found as a monomer or as a polymer, including cellulose, starch, glycogen and others. Hexoses importance resides in their variety of functions. They are structural components for all living cells, glucose is an important metabolic substrate, serves as a precursor for synthesis of many other molecules, and the most important function shared with related hexoses, is that it is the first fuel used by most organisms in all three kingdoms serving as quick substrate for energy production in the form of ATP through glycolysis and the subsequent metabolic pathways.In higher organisms, glucose is mainly obtained directly from the diet when disaccharides and polysaccharides are hydrolyzed. After that, glucose needs to travel a long way to reach the target cells to be metabolized or stored. The first step is the transfer from the lumen of the small intestine to epithelium cells, followed by transport by blood circulation to each organ, tissue and cell. Due to the hydrophilic nature, these processes involve the transfer of glucose (and other hexoses) across the biological lipid bi-layer plasma cell membranes (Wilson-O'Brien et al. 2010).This transport is mediated by integral transporter proteins which are classified based on phylogenetic and functional data (Wilson-O'Brien et al. 2010). Thus the hexose transporters belong to one of two protein super families: the sodium/solute symporter family (SSSF; (Reizer et al. 1994)) and the major facilitative super-family (MFS; (Marger and Saier Jr, 1993; Pao et al. 1998; Saier Jr, 2000)) whose Pfam numbers in the database http://pfam.janelia.org are PF00474 and CL0015 respectively.

Characterization, fluctuation and tissue differences in nutrient content in the Pacific oyster ( Crassostrea gigas ) in Qingdao, northern China

“…GSK and PBK expression patterns were nearly the same as those for GP and GDE, which may reflect their regulatory function of glycogen metabolism. Hexokinase and GLUT expression was consistent with that of GS, which provides glycogen synthesis precursors (Martínez-Quintana & Yepiz-Plascencia, 2012;Zeng, Ni, & Ke, 2015). Pyruvate kinase, PFK and PGK in the glycolysis pathway had similar expression patterns as those for GP and GDE, which may reflect their whereabouts after glycogen decomposition.…”

Interrelationship Between Contractility, Protein Synthesis and Metabolism in Mantle of Juvenile Cuttlefish (Sepia officinalis)

“…The questions are “how can such a high intracellular to extracellular glucose gradient be maintained” and “where is the increased glucose in the media coming from.” There is preliminary evidence for an active glucose uptake by mantle of the Japanese oyster ( Crassostrea gigas ) (Bamford and Gingles, 1974) and a Na + coupled, active transport of glucose, occurs in frog skeletal muscle (Kitasato and Marunaka, 1985). Given that glucose uptake has been little studied in marine invertebrates (Martínez-Quintana and Yepiz-Plascencia, 2012), the possibility of active glucose uptake by mantle of S. officinalis should be considered. Impairment of glycolysis with IAA could lead to a negative cascade whereby membrane based Na + –K + ATPase would be compromised, and in turn impairing the ability to maintain an elevated intracellular glucose level leading to a movement of glucose down its concentration gradient and an increase in media glucose.…”

Transcriptomic analysis of thermotolerant Artemia franciscana populations shows that thermal adaptation affects expression and regulation of metabolism-, stress-, and immune-related genes

“…The major facilitator superfamily (MEF) was upregulated as a molecule involved in monocarboxylate and glucose transporters 41 . Glucose is the rst important metabolic substrate that provides quick fuel for most organisms in the form of ATP through glycolysis pathways 42 . Ferritin involved in iron metabolism was upregulated in SITT.…”