Varied Mechanisms Underlie the Free Sialic Acid Storage Disorders

Wreden, Christopher; Wlizla, Marcin; Reimer, Richard J.

doi:10.1074/jbc.m411295200

Cited by 72 publications

(89 citation statements)

References 45 publications

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“…3 E-G). Importantly, expression of the sialin mutant L22A-L23A, which reportedly is targeted to the plasma membrane (24,25), increased the currents by approximately twofold with either NO 3 − or SA in the external solution ( Fig. 3 H and I).…”

Section: Sialin Mediates Nomentioning

confidence: 93%

“…To establish the link between sialin and nitrate transport, we examined the effect of two nonfunctional sialin mutants that have been associated with Salla disease (R39C) and ISSD (H183R) (23)(24)(25). Expression of each of these mutants in HSG cells induced dominant suppression of both NO 3 − and SA − currents without altering the current-voltage (I-V) characteristics (Fig.…”

Section: Assessment Of Sialin-mediated No 3 − Transport In Fibroblastmentioning

confidence: 99%

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Sialin ( SLC17A5 ) functions as a nitrate transporter in the plasma membrane

Qin

Liu

Sun

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

174

142

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In vivo recycling of nitrate (NO 3 − ) and nitrite (NO 2 − ) is an important alternative pathway for the generation of nitric oxide (NO) and maintenance of systemic nitrate–nitrite–NO balance. More than 25% of the circulating NO 3 − is actively removed and secreted by salivary glands. Oral commensal bacteria convert salivary NO 3 − to NO 2 − , which enters circulation and leads to NO generation. The transporters for NO 3 − in salivary glands have not yet been identified. Here we report that sialin ( SLC17A 5 ), mutations in which cause Salla disease and infantile sialic acid storage disorder (ISSD), functions as an electrogenic 2NO 3 − /H + cotransporter in the plasma membrane of salivary gland acinar cells. We have identified an extracellular pH-dependent anion current that is carried by NO 3 − or sialic acid (SA), but not by Br − , and is accompanied by intracellular acidification. Both responses were reduced by knockdown of sialin expression and increased by the plasma membrane-targeted sialin mutant (L22A-L23A). Fibroblasts from patients with ISSD displayed reduced SA- and NO 3 − -induced currents compared with healthy controls. Furthermore, expression of disease-associated sialin mutants in fibroblasts and salivary gland cells suppressed the H + -dependent NO 3 − conductance. Importantly, adenovirus-dependent expression of the sialinH183R mutant in vivo in pig salivary glands decreased NO 3 − secretion in saliva after intake of a NO 3 − -rich diet. Taken together, these data demonstrate that sialin mediates nitrate influx into salivary gland and other cell types. We suggest that the 2NO 3 − /H + transport function of sialin in salivary glands can contribute significantly to clearance of serum nitrate, as well as nitrate recycling and physiological nitrite-NO homeostasis.

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Section: Sialin Mediates Nomentioning

confidence: 93%

Section: Assessment Of Sialin-mediated No 3 − Transport In Fibroblastmentioning

confidence: 99%

Sialin ( SLC17A5 ) functions as a nitrate transporter in the plasma membrane

Qin

Liu

Sun

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

174

142

View full text Add to dashboard Cite

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“…The lysosomal transporter sialin was first identified through genetic studies of the human free sialic acid storage disorders, Salla disease and infantile sialic acid storage disorder, a group of diseases in which the sialic acid N-acetylneuraminic acid (NANA) 2 and glucuronic acid (GlcUA) accumulate in lysosomes (1). These acidic sugars are normally transported out of the lysosome after they are released during degradation of glycolipids and glycoproteins.…”

mentioning

confidence: 99%

Structure-Function Studies of the SLC17 Transporter Sialin Identify Crucial Residues and Substrate-induced Conformational Changes

Courville

Quick

Reimer

2010

Journal of Biological Chemistry

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Salla disease and infantile sialic acid storage disorder are human diseases caused by loss of function of sialin, a lysosomal transporter that mediates H ؉ -coupled symport of acidic sugars N-acetylneuraminic acid and glucuronic acid out of lysosomes. Along with the closely related vesicular glutamate transporters, sialin belongs to the SLC17 transporter family. Despite their critical role in health and disease, these proteins remain poorly understood both structurally and mechanistically. Here, we use substituted cysteine accessibility screening and radiotracer flux assays to evaluate experimentally a computationally generated three-dimensional structure model of sialin. According to this model, sialin consists of 12 transmembrane helices (TMs) with an overall architecture similar to that of the distantly related glycerol 3-phosphate transporter GlpT. We show that TM4 in sialin lines a large aqueous cavity that forms a part of the substrate permeation pathway and demonstrate substrate-induced alterations in accessibility of substituted cysteine residues in TM4.In addition, we demonstrate that one mutant, F179C, has a dramatically different effect on the apparent affinity and transport rate for N-acetylneuraminic acid and glucuronic acid, suggesting that it may be directly involved in substrate recognition and/or translocation. These findings offer a basis for further defining the transport mechanism of sialin and other SLC17 family members.

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“…Moreover, it is frequently observed that mutations disturb targeting of the protein to the correct cellular organelle. For instance, sialin, another member of the SLC17 family, is a lysosomal sialic acid/H ϩ co-transporter and targeted to the plasma membrane when mutations are introduced into its dileucine motif (21,22). Because the VGLUT assay procedure is based on the assumption that the transporter is targeted to acidic organelles and that endogenous ATP fully energizes V-ATPase to drive the uptake, it is not certain whether this assay is valid for mutant VGLUT.…”

mentioning

confidence: 99%

Vesicular Glutamate Transporter Contains Two Independent Transport Machineries

Juge

Yoshida

Yatsushiro

et al. 2006

Journal of Biological Chemistry

108

193

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Vesicular glutamate transporters (VGLUTs) are responsible for the vesicular storage of L-glutamate and play an essential role in glutamatergic signal transmission in the central nervous system. The molecular mechanism of the transport remains unknown. Here, we established a novel in vitro assay procedure, which includes purification of wild and mutant VGLUT2 and their reconstitution with purified bacterial F o F 1 -ATPase (F-ATPase) into liposomes. Upon the addition of ATP, the proteoliposomes facilitated L-glutamate uptake in a membrane potential (⌬)-dependent fashion. The ATP-dependent L-glutamate uptake exhibited an absolute requirement for ϳ4 mM Cl ؊ , was sensitive to Evans blue, but was insensitive to D,L-aspartate. VGLUT2s with mutations in the transmembrane-located residues Arg 184 , His 128 , and Glu 191 showed a dramatic loss in L-glutamate transport activity, whereas Na ؉ -dependent inorganic phosphate (P i ) uptake remained comparable to that of the wild type. Furthermore, P i transport did not require Cl ؊ and was not inhibited by Evans blue. Thus, VGLUT2 appears to possess two intrinsic transport machineries that are independent of each other: a ⌬-dependent L-glutamate uptake and a Na ؉ -dependent P i uptake.Vesicular storage and subsequent exocytosis of L-glutamate is the major pathway for excitatory signal transmission in the central nervous system (1-3). Vesicular glutamate transporters (VGLUTs) 2 are essential for the vesicular storage of L-glutamate through active transport of L-glutamate into synaptic vesicles at the expense of ⌬H ϩ established by vacuolar H ϩ -ATPase (V-ATPase) (1). There are three isoforms of VGLUT, denoted VGLUT1, VGLUT2, and VGLUT3 on the basis of the order of their discovery (2, 4 -6). VGLUT1 and VGLUT2 show a complementary expression pattern in essentially all known glutamatergic neurons, suggesting that the two VGLUTs are involved in glutamatergic neurotransmission (7-9). In fact, VGLUT1 knock-out mice exhibit a loss of secretion of L-glutamate and glutamatergic neurotransmission in neurons that normally express VGLUT1 (4, 10). In contrast, VGLUT3 is expressed in neurons that are usually classified as non-glutamatergic neurons and astrocytes suggesting the involvement of VGLUT3 in a novel mode of L-glutamate signaling (11-13). VGLUTs are also expressed in peripheral nonneuronal cells, associated with a wide variety of secretory vesicles and are responsible for glutamate-mediated regulation in various cellular processes (5).VGLUTs belong to the SLC17/type I anion transport family, one of the major facilitator superfamilies (MFS), and are not related to other neurotransmitter transporters such as vesicular acetylcholine transporter and vesicular monoamine transporter (2, 14). VGLUT exhibits unique transport properties when compared with other vesicular neurotransmitter transporters. For one, VGLUT is activated by low concentrations of Cl Ϫ (ϳ4 mM) through a putative Cl Ϫ binding site (15-18). Furthermore, VGLUT requires membrane potential (positive inside) as a driving...

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Varied Mechanisms Underlie the Free Sialic Acid Storage Disorders

Cited by 72 publications

References 45 publications

Sialin ( SLC17A5 ) functions as a nitrate transporter in the plasma membrane

Sialin ( SLC17A5 ) functions as a nitrate transporter in the plasma membrane

Structure-Function Studies of the SLC17 Transporter Sialin Identify Crucial Residues and Substrate-induced Conformational Changes

Vesicular Glutamate Transporter Contains Two Independent Transport Machineries

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