Synergistic Anion and Metal Binding to the Ferric Ion-binding Protein from Neisseria gonorrhoeae

Guo, Maolin; Harvey, Ian; Yang, Weiping; Coghill, Lorraine S.; Campopiano, Dominic J.; Parkinson, John A.; MacGillivray, Ross T. A.; Harris, Wesley R.; Sadler, Peter J.

doi:10.1074/jbc.m208776200

Cited by 67 publications

(70 citation statements)

References 64 publications

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“…ZnuA, FutA1) that bind their ligand with a K d of Ͻ10 Ϫ6 M. Concomitant binding of both metal and anion has been observed with other periplasmic-binding proteins. Synergistic Fe 3ϩ binding with phosphate or CO 3 Ϫ has been observed for both the Haemophilus influenzae and Neisseria gonorrhoeae periplasmic ferric-binding proteins (23,24). The crystal structures of these proteins complexed with Fe 3ϩ and phosphate show that the anion not only contributes to the coordination sphere of the metal but makes multiple hydrogen bonds and electrostatic interactions with the protein as well (25,26).…”

Section: Discussionmentioning

confidence: 94%

The Structure of a Cyanobacterial Bicarbonate Transport Protein, CmpA

Koropatkin

Koppenaal

Pakrasi

et al. 2007

Journal of Biological Chemistry

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Cyanobacteria, blue-green algae, are the most abundant autotrophs in aquatic environments and form the base of the food chain by fixing carbon and nitrogen into cellular biomass. To compensate for the low selectivity of Rubisco for CO 2 over O 2 , cyanobacteria have developed highly efficient CO 2 -concentrating machinery of which the ABC transport system CmpABCD from Synechocystis PCC 6803 is one component. Here, we have described the structure of the bicarbonatebinding protein CmpA in the absence and presence of bicarbonate and carbonic acid. CmpA is highly homologous to the nitrate transport protein NrtA. CmpA binds carbonic acid at the entrance to the ligand-binding pocket, whereas bicarbonate binds in nearly an identical location compared with nitrate binding to NrtA. Unexpectedly, bicarbonate binding is accompanied by a metal ion, identified as Ca 2؉ via inductively coupled plasma optical emission spectrometry. The binding of bicarbonate and metal appears to be highly cooperative and suggests that CmpA may co-transport bicarbonate and calcium or that calcium acts a cofactor in bicarbonate transport.Cyanobacteria are the most abundant microorganisms in aquatic environments and play a key role in the global carbon cycle (1). It is estimated that these photosynthetic microbes are responsible for ϳ50% of carbon fixation in the oceans. Over their 2.7-billion-year existence, cyanobacteria had to adapt to a changing gaseous environment where the levels of CO 2 declined and O 2 increased (2). Because O 2 can compete with CO 2 for binding to the carbon-fixing enzyme Rubisco (3), cyanobacteria evolved the most effective CO 2 -concentrating mechanism (CCM) 2 that allows them to concentrate CO 2 levels around Rubisco up to 1000-fold. The CCM involves the import and accumulation of inorganic carbon as HCO 3 Ϫ in the cytoplasm and subsequent conversion to CO 2 in the protein microcompartment called the "carboxysome" via carbonic anhydrase.One component of this CCM machinery in Synechocystis PCC 6803 is the cmpABCD operon that encodes a high affinity bicarbonate ABC transporter that is induced under low CO 2 conditions (4). This transporter is composed of four polypeptides, a high affinity solute-binding lipoprotein (CmpA), an integral membrane permease (CmpB), a cytoplasmic ATPase (CmpD), and an ATPase/solute-binding fusion protein (CmpC) that regulates transport (Fig. 1). The CmpABCD transporter is the highest affinity bicarbonate transporter of cyanobacteria (4). This affinity is predominantly conferred by the binding of bicarbonate to CmpA (K d ϭ 5 M) (5). CmpA is anchored to the periplasmic face of the cytoplasmic membrane via a lipid anchor attached to a conserved cysteine (6). The closest known homologue of CmpA is NrtA, the solute-binding protein of the nitrate-specific NrtABCD transporter that is 48% identical and 61% similar in amino acid sequence (7). We recently published an analysis (8) of the 1.6-Å structure of NrtA complexed with nitrate to elucidate the molecular determinants of nitrate specificity. From ...

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Section: Discussionmentioning

confidence: 94%

The Structure of a Cyanobacterial Bicarbonate Transport Protein, CmpA

Koropatkin

Koppenaal

Pakrasi

et al. 2007

Journal of Biological Chemistry

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“…These interactions also likely improve iron-tyrosine interactions by increasing the electronegativity of the tyrosine hydroxyls. Unlike the periplasmic iron-binding proteins from Neisseria gonorrhoeae (nFbpA) (22) and Haemophilus influenzae (HiFbpA) (23), there are no apparent anion interactions with the bound iron. The only non-protein atom in the immediate vicinity of the iron is an apparent water molecule that interacts with the Tyr-242 hydroxyl and a sulfate molecule that interacts with that water molecule and the imidazole ring of His-54.…”

Section: Resultsmentioning

confidence: 99%

“…Here, two tyrosines and one oxygen from the carbonate form a distorted trigonal plane with the second carbonate oxygen and the third tyrosine residues lying above and below this plane. Unlike the anion-dependent binding of ferric ions to the iron-transport protein from N. gonorrhoeae (22), MhFbpA can still bind iron in the absence of anion. However the solute binding cleft is open in the absence of anion in the case of MhFbpA.…”

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confidence: 99%

The Structure of the Iron-binding Protein, FutA1, from Synechocystis 6803

Koropatkin

Randich

Bhattacharyya-Pakrasi

et al. 2007

Journal of Biological Chemistry

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Cyanobacteria account for a significant percentage of aquatic primary productivity even in areas where the concentrations of essential micronutrients are extremely low. To better understand the mechanism of iron selectivity and transport, the structure of the solute binding domain of an ATP binding cassette iron transporter, FutA1, was determined in the presence and absence of iron. The iron ion is bound within the "C-clamp" structure via four tyrosine and one histidine residues. There are extensive interactions between these ligating residues and the rest of the protein such that the conformations of the side chains remain relatively unchanged as the iron is released by the opening of the metal binding cleft. This is in stark contrast to the zinc-binding protein, ZnuA, where the domains of the metalbinding protein remain relatively fixed, whereas the ligating residues rotate out of the binding pocket upon metal release. The rotation of the domains in FutA1 is facilitated by two flexible ␤-strands running along the back of the protein that act like a hinge during domain motion. This motion may require relatively little energy since total contact area between the domains is the same whether the protein is in the open or closed conformation. Consistent with the pH dependence of iron binding, the main trigger for iron release is likely the histidine in the ironbinding site. Finally, neither FutA1 nor FutA2 binds iron as a siderophore complex or in the presence of anions, and both preferentially bind ferrous over ferric ions.Bioavailable iron is a limiting nutrient for primary production in large areas of the oceans. This concentration of free iron in aquatic environments is dynamic and varies greatly depending upon the local environment. Fe 3ϩ is notoriously insoluble in water at neutral pH values, whereas Fe 2ϩ is very soluble but highly susceptible to oxidation by atmospheric oxygen. Microbes play a large role in the cycling of iron between the ferric and ferrous forms and generally reduce ferric iron under anaerobic conditions by using it as a final electron acceptor. Conversely, microbes can oxidize ferrous iron under aerobic conditions when other compounds such as nitrate are the final electron acceptors. Organisms can import either form of iron. A number of bacteria, algae, and Cyanobacteria increase the bioavailability of ferric iron through the secretion of organic molecules, such as siderophores, into the extracellular environment. These compounds have exceptionally high binding affinities for iron (association constants of ϳ10 MϪ1 ) and essentially scavenge ferric iron from the extracellular environment before the organism imports the entire complex into the cell (e.g. Ref. 1). In some cases these siderophores may actually facilitate a photochemical reduction of the bound ferric ion (2). Alternatively, ferric iron can be locally reduced to the more soluble ferrous form and imported directly. This latter can be accomplished by the organisms itself as is the case with some algal species that use ferric chel...

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“…Model Building and Refinement-The EXAFS data were processed and analyzed as described previously (19) using full (three-dimensional) multiple scattering. We used our model of the zinc site (17), based on a published crystal structure at 2.5 Å of ligand-free (apo)albumin (Protein Data Bank code 1AO6 (9)), as a starting point for EXAFS data refinement.…”

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confidence: 99%