Possible Roles for His 208 in the Active-Site Region of Chloroplast Carbonic Anhydrase fromPisum sativum

Björkbacka, Harry; Johansson, Ingvar; Forsman, Cecilia

doi:10.1006/abbi.1998.0961

Cited by 19 publications

(11 citation statements)

References 39 publications

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“…in the direction of Tyr205′ OH. This path would be consistent with the observation that mutations in His209 result in a much lower effective K buffer (Björkbacka et al ., 1999), as this residue is located near Tyr205 and may form part of a non‐specific buffer binding site.…”

Section: Resultssupporting

confidence: 91%

The active site architecture of Pisum sativum beta -carbonic anhydrase is a mirror image of that of alpha -carbonic anhydrases

2000

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We have determined the structure of the beta-carbonic anhydrase from the dicotyledonous plant Pisum sativum at 1.93 A resolution, using a combination of multiple anomalous scattering off the active site zinc ion and non-crystallographic symmetry averaging. The mol- ecule assembles as an octamer with a novel dimer of dimers of dimers arrangement. Two distinct patterns of conservation of active site residues are observed, implying two potentially mechanistically distinct classes of beta-carbonic anhydrases. The active site is located at the interface between two monomers, with Cys160, His220 and Cys223 binding the catalytic zinc ion and residues Asp162 (oriented by Arg164), Gly224, Gln151, Val184, Phe179 and Tyr205 interacting with the substrate analogue, acetic acid. The substrate binding groups have a one to one correspondence with the functional groups in the alpha-carbonic anhydrase active site, with the corresponding residues being closely superimposable by a mirror plane. Therefore, despite differing folds, alpha- and beta-carbonic anhydrase have converged upon a very similar active site design and are likely to share a common mechanism.

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Section: Resultssupporting

confidence: 91%

The active site architecture of Pisum sativum beta -carbonic anhydrase is a mirror image of that of alpha -carbonic anhydrases

2000

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“…On the basis of the kinetic data, it was suggested that two conserved residues, Tyr-88 and His-92 in Co -CA, (His-208 and Tyr-205 in pea β-CA, respectively), play the role of proton shuttle in β-CA [11]. Mutagenesis studies also support that these residues are involved in proton transport [25], [48]. Interestingly, we found that binding of inhibitors to Co -CA is mediated by side-chain movements of both residues Tyr-88′ and His-92′.…”

Section: Discussionmentioning

confidence: 99%

Structural Studies of β-Carbonic Anhydrase from the Green Alga Coccomyxa: Inhibitor Complexes with Anions and Acetazolamide

et al. 2011

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The β-class carbonic anhydrases (β-CAs) are widely distributed among lower eukaryotes, prokaryotes, archaea, and plants. Like all CAs, the β-enzymes catalyze an important physiological reaction, namely the interconversion between carbon dioxide and bicarbonate. In plants the enzyme plays an important role in carbon fixation and metabolism. To further explore the structure-function relationship of β-CA, we have determined the crystal structures of the photoautotroph unicellular green alga Coccomyxa β-CA in complex with five different inhibitors: acetazolamide, thiocyanate, azide, iodide, and phosphate ions. The tetrameric Coccomyxa β-CA structure is similar to other β-CAs but it has a 15 amino acid extension in the C-terminal end, which stabilizes the tetramer by strengthening the interface. Four of the five inhibitors bind in a manner similar to what is found in complexes with α-type CAs. Iodide ions, however, make contact to the zinc ion via a zinc-bound water molecule or hydroxide ion — a type of binding mode not previously observed in any CA. Binding of inhibitors to Coccomyxa β-CA is mediated by side-chain movements of the conserved residue Tyr-88, extending the width of the active site cavity with 1.5-1.8 Å. Structural analysis and comparisons with other α- and β-class members suggest a catalytic mechanism in which the movements of Tyr-88 are important for the CO2-HCO3 - interconversion, whereas a structurally conserved water molecule that bridges residues Tyr-88 and Gln-38, seems important for proton transfer, linking water molecules from the zinc-bound water to His-92 and buffer molecules.

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“…The k cat /K M value for CO 2 in pea extracts has been measured for a pH range of 6-9 and at 25 • C (Bjorkbacka et al, 1999). The pH response described a similar pattern as the one found for Arabidopsis by Rowlett et al (2002) (Fig.…”

Section: Can the Proposed Model Explain Observations Realistically?mentioning

confidence: 99%

A new mechanistic framework to predict OCS fluxes from soils

Ogée¹,

et al. 2016

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Abstract.Estimates of photosynthetic and respiratory fluxes at large scales are needed to improve our predictions of the current and future global CO 2 cycle. Carbonyl sulfide (OCS) is the most abundant sulfur gas in the atmosphere and has been proposed as a new tracer of photosynthetic gross primary productivity (GPP), as the uptake of OCS from the atmosphere is dominated by the activity of carbonic anhydrase (CA), an enzyme abundant in leaves that also catalyses CO 2 hydration during photosynthesis. However soils also exchange OCS with the atmosphere, which complicates the retrieval of GPP from atmospheric budgets. Indeed soils can take up large amounts of OCS from the atmosphere as soil microorganisms also contain CA, and OCS emissions from soils have been reported in agricultural fields or anoxic soils. To date no mechanistic framework exists to describe this exchange of OCS between soils and the atmosphere, but empirical results, once upscaled to the global scale, indicate that OCS consumption by soils dominates OCS emission and its contribution to the atmospheric budget is large, at about one third of the OCS uptake by vegetation, also with a large uncertainty. Here, we propose a new mechanistic model of the exchange of OCS between soils and the atmosphere that builds on our knowledge of soil CA activity from CO 2 oxygen isotopes. In this model the OCS soil budget is described by a first-order reaction-diffusion-production equation, assuming that the hydrolysis of OCS by CA is total and irreversible. Using this model we are able to explain the observed presence of an optimum temperature for soil OCS uptake and show how this optimum can shift to cooler temperatures in the presence of soil OCS emission. Our model can also explain the observed optimum with soil moisture content previously described in the literature as a result of diffusional constraints on OCS hydrolysis. These diffusional constraints are also responsible for the response of OCS uptake to soil weight and depth observed previously. In order to simulate the exact OCS uptake rates and patterns observed on several soils collected from a range of biomes, different CA activities had to be invoked in each soil type, coherent with expected physiological levels of CA in soil microbes and with CA activities derived from CO 2 isotope exchange measurements, given the differences in affinity of CA for both trace gases. Our model can be used to help upscale laboratory measurements to the plot or the region. Several suggestions are given for future experiments in order to test the model further and allow a better constraint on the large-scale OCS fluxes from both oxic and anoxic soils.

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Possible Roles for His 208 in the Active-Site Region of Chloroplast Carbonic Anhydrase fromPisum sativum

Cited by 19 publications

References 39 publications

The active site architecture of Pisum sativum beta -carbonic anhydrase is a mirror image of that of alpha -carbonic anhydrases

The active site architecture of Pisum sativum beta -carbonic anhydrase is a mirror image of that of alpha -carbonic anhydrases

Structural Studies of β-Carbonic Anhydrase from the Green Alga Coccomyxa: Inhibitor Complexes with Anions and Acetazolamide

A new mechanistic framework to predict OCS fluxes from soils

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