Structural and mechanistic diversity of secondary transporters

Sobczak, Iwona; Lolkema, Juke S.

doi:10.1016/j.mib.2005.02.005

Cited by 37 publications

(31 citation statements)

References 39 publications

(35 reference statements)

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“…Like the 2HCT transporters, the NaCX exchangers are believed to be built of two domains of five TMSs. However, the pore-loops are between the second and third TMSs in each domain rather than between the fourth and fifth as in the 2HCT family (137). Possibly these structural variations represent similar translocation mechanisms.…”

Section: Structural Modelmentioning

confidence: 97%

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The 2-Hydroxycarboxylate Transporter Family: Physiology, Structure, and Mechanism

Sobczak

Lolkema

2005

Microbiol Mol Biol Rev

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SUMMARY The 2-hydroxycarboxylate transporter family is a family of secondary transporters found exclusively in the bacterial kingdom. They function in the metabolism of the di- and tricarboxylates malate and citrate, mostly in fermentative pathways involving decarboxylation of malate or oxaloacetate. These pathways are found in the class Bacillales of the low-CG gram-positive bacteria and in the gamma subdivision of the Proteobacteria. The pathways have evolved into a remarkable diversity in terms of the combinations of enzymes and transporters that built the pathways and of energy conservation mechanisms. The transporter family includes H+ and Na+ symporters and precursor/product exchangers. The proteins consist of a bundle of 11 transmembrane helices formed from two homologous domains containing five transmembrane segments each, plus one additional segment at the N terminus. The two domains have opposite orientations in the membrane and contain a pore-loop or reentrant loop structure between the fourth and fifth transmembrane segments. The two pore-loops enter the membrane from opposite sides and are believed to be part of the translocation site. The binding site is located asymmetrically in the membrane, close to the interface of membrane and cytoplasm. The binding site in the translocation pore is believed to be alternatively exposed to the internal and external media. The proposed structure of the 2HCT transporters is different from any known structure of a membrane protein and represents a new structural class of secondary transporters.

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Section: Structural Modelmentioning

confidence: 97%

“…These structures have provided a first glimpse of the structural and mechanistic diversity that may be present in the many different families of secondary transporters. The structures of the drug transporter AcrB, the lactose transporter LacY, the glycerol-P/P i exchanger GlpT (137).…”

Section: Introductionmentioning

confidence: 99%

The 2-Hydroxycarboxylate Transporter Family: Physiology, Structure, and Mechanism

Sobczak

Lolkema

2005

Microbiol Mol Biol Rev

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“…The AmtB protein consists of 428 amino acids (139), but in E. coli, the 22 N-terminal residues are removed upon insertion of the protein into the membrane (271). The first and second five trans-membrane segments form structurally homologous domains, whereas the 11th segment is not part of this domain structure (272). Upon purification, the protein is obtained as a homotrimer, even in a detergent solution (273).…”

Section: Ammonium Transportermentioning

confidence: 99%

Nitrogen Assimilation in Escherichia coli: Putting Molecular Data into a Systems Perspective

Heeswijk¹,

Westerhoff

Boogerd³

2013

Microbiol Mol Biol Rev

228

246

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SUMMARY We present a comprehensive overview of the hierarchical network of intracellular processes revolving around central nitrogen metabolism in Escherichia coli . The hierarchy intertwines transport, metabolism, signaling leading to posttranslational modification, and transcription. The protein components of the network include an ammonium transporter (AmtB), a glutamine transporter (GlnHPQ), two ammonium assimilation pathways (glutamine synthetase [GS]-glutamate synthase [glutamine 2-oxoglutarate amidotransferase {GOGAT}] and glutamate dehydrogenase [GDH]), the two bifunctional enzymes adenylyl transferase/adenylyl-removing enzyme (ATase) and uridylyl transferase/uridylyl-removing enzyme (UTase), the two trimeric signal transduction proteins (GlnB and GlnK), the two-component regulatory system composed of the histidine protein kinase nitrogen regulator II (NRII) and the response nitrogen regulator I (NRI), three global transcriptional regulators called nitrogen assimilation control (Nac) protein, leucine-responsive regulatory protein (Lrp), and cyclic AMP (cAMP) receptor protein (Crp), the glutaminases, and the nitrogen-phosphotransferase system. First, the structural and molecular knowledge on these proteins is reviewed. Thereafter, the activities of the components as they engage together in transport, metabolism, signal transduction, and transcription and their regulation are discussed. Next, old and new molecular data and physiological data are put into a common perspective on integral cellular functioning, especially with the aim of resolving counterintuitive or paradoxical processes featured in nitrogen assimilation. Finally, we articulate what still remains to be discovered and what general lessons can be learned from the vast amounts of data that are available now.

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“…secondary transport | symmetry | membrane protein | alkali metal ion | osmoregulation S econdary transporters constitute an important class of membrane proteins that use the free energy stored in ionconcentration gradients to drive the transport of various molecules across membranes (1,2). In recent years a number of X-ray crystallographic structures of secondary transporters have been reported, providing compelling support for the long-standing alternating-access hypothesis (reviewed in ref.…”

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confidence: 95%

Investigation of the sodium-binding sites in the sodium-coupled betaine transporter BetP

Khafizov¹,

Pérez²,

Koshy³

et al. 2012

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

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Sodium-coupled substrate transport plays a central role in many biological processes. However, despite knowledge of the structures of several sodium-coupled transporters, the location of the sodiumbinding site(s) often remains unclear. Several of these structures have the five transmembrane-helix inverted-topology repeat, LeuTlike (FIRL) fold, whose pseudosymmetry has been proposed to facilitate the alternating-access mechanism required for transport. Here, we provide biophysical, biochemical, and computational evidence for the location of the two cation-binding sites in the sodium-coupled betaine symporter BetP. A recent X-ray structure of BetP in a sodium-bound closed state revealed that one of these sites, equivalent to the Na2 site in related transporters, is located between transmembrane helices 1 and 8 of the FIRL-fold; here, we confirm the location of this site by other means. Based on the pseudosymmetry of this fold, we hypothesized that the second site is located between the equivalent helices 6 and 3. Molecular dynamics simulations of the closed-state structure suggest this second sodium site involves two threonine sidechains and a backbone carbonyl from helix 3, a phenylalanine from helix 6, and a water molecule. Mutating the residues proposed to form the two binding sites increased the apparent K m and K d for sodium, as measured by betaine uptake, tryptophan fluorescence, and 22 Na + binding, and also diminished the transient currents measured in proteoliposomes using solid supported membrane-based electrophysiology. Taken together, these results provide strong evidence for the identity of the residues forming the sodium-binding sites in BetP.secondary transport | symmetry | membrane protein | alkali metal ion | osmoregulation

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Structural and mechanistic diversity of secondary transporters

Cited by 37 publications

References 39 publications

The 2-Hydroxycarboxylate Transporter Family: Physiology, Structure, and Mechanism

The 2-Hydroxycarboxylate Transporter Family: Physiology, Structure, and Mechanism

Nitrogen Assimilation in Escherichia coli: Putting Molecular Data into a Systems Perspective

Investigation of the sodium-binding sites in the sodium-coupled betaine transporter BetP

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