| 1. |
- Feil, S. C., et al.
(författare)
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Crystallization and preliminary X-ray analysis of glutathione transferases from cyanobacteria
- 2009
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Ingår i: Acta Crystallographica. Section F. - 1744-3091 .- 1744-3091. ; 65, s. 475-477
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Tidskriftsartikel (refereegranskat)abstract
- Glutathione S-transferases (GSTs) are a group of multifunctional enzymes that are found in animals, plants and microorganisms. Their primary function is to remove toxins derived from exogenous sources or the products of metabolism from the cell. Mammalian GSTs have been extensively studied, in contrast to bacterial GSTs which have received relatively scant attention. A new class of GSTs called Chi has recently been identified in cyanobacteria. Chi GSTs exhibit a high glutathionylation activity towards isothiocyanates, compounds that are normally found in plants. Here, the crystallization of two GSTs are presented: TeGST produced by Thermosynechococcus elongates BP-1 and SeGST from Synechococcus elongates PCC 6301. Both enzymes formed crystals that diffracted to high resolution and appeared to be suitable for further X-ray diffraction studies. The structures of these GSTs may shed further light on the evolution of GST catalytic activity and in particular why these enzymes possess catalytic activity towards plant antimicrobial compounds.
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| 2. |
- Ivarsson, Ylva, 1976-
(författare)
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Evolutionary Analysis and Posttranslational Chemical Modifications in Protein Redesign : A Study on Mu Class Glutathione Transferases
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Glutathione transferases (GSTs) constitute a family of multifarious enzymes that conjugate glutathione (GSH) with a wide range of electrophiles. GSTs are grouped into different classes based on protein sequence similarities. Despite high sequence identities between GSTs of the same class they often display different substrate specificites. Human GST M1-1 is efficiently catalyzing the conjugation of GSH and various epoxide substrates, whereas the 84% sequence-identical GST M2-2 has low activities with the same substrates.Evolutionary rate analysis was used to identify hypervariable amino acid positions among GST Mu class sequences. A Thr to Ser conversion of the variable residue 210 in GST M2-2 elicited a drastic increase in catalytic activity with epoxides, which is the characteristic activity of GST M1-1. This provides support for the usefulness of evolutionary analysis in identifying functionally important residues, although the additional mutations of two other variable residues did not confer any noteworthy changes in activity.To further investigate the functional importance of residue T210 in GST M2-2 it was replaced by all other commonly occurring amino acids. The replacements caused marked changes in substrate specificity, stability, and expressivity, indicating how functionalities of a duplicated Mu class GST may easily be altered by point mutations. The stereo- and regioselectivity in epoxide-conjugation catalyzed by GSTs M1-1 and M2-2 was investigated. The results show that a serine in position 210 is beneficial for high enantioselectivity with trans-stilbene oxide. However, an alanine in position 210 is more favorable for stereo- and regioselectivity with the smaller epoxide substrate styrene-7,8-oxide. The low enantioselectivity of GST M1-1 was improved 10- and 9- fold with styrene-7,8-oxide and 1-phenylpropylene oxide, respectively, through different combination of site-specific mutations and posttranslational chemical modifications. The approach can be employed in more extensive screening experiments where a large variety of modifications easily can be tested.
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| 3. |
- Wiktelius, Eric, et al.
(författare)
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Novel class of glutathione transferases from cyanobacteria exhibit high catalytic activities towards naturally occurring isothiocyanates
- 2007
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Ingår i: Biochemical Journal. - 0264-6021 .- 1470-8728. ; 406, s. 115-123
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Tidskriftsartikel (refereegranskat)abstract
- In the present paper, we report a novel class of GSTs (glutathione transferases), called the Chi class, originating from cyanobacteria and with properties not observed previously in prokaryotic enzymes. GSTs constitute a widespread multifunctional group of proteins, of which mammalian enzymes are the best characterized. Although GSTs have their origin in prokaryotes, few bacterial representatives have been characterized in detail, and the catalytic activities and substrate specificities observed have generally been very modest. The few well-studied bacterial GSTs have largely unknown physiological functions. Genome databases reveal that cyanobacteria have an extensive arsenal of glutathione-associated proteins. We have studied two cyanobacterial GSTs which are the first examples of bacterial enzymes that are as catalytically efficient as the best mammalian enzymes. GSTs from the thermophile Thermosynechococcus elongatus BP-1 and from Synechococcus elongatus PCC 6301 were found to catalyse the conjugation of naturally occurring plant-derived isothiocyanates to glutathione at high rates. The cyanobacterial GSTs studied are smaller than previously described members of this enzyme family, but display many of the typical structural features that are characteristics of GSTs. They are also active towards several classical substrates, but at the same moderate rates that have been observed for other GSTs derived from prokaryotes. The cloning, expression and characterization of two cyanobacterial GSTs are described. The possible significance of the observed catalytic properties is discussed in the context of physiological relevance and GST evolution.
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