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- 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. |
- Pleijel, Håkan, 1958, et al.
(författare)
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Differential ozone sensitivity in an old and a modem Swedish wheat cultivar - grain yield and quality, leaf chlorophyll and stomatal conductance
- 2006
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Ingår i: Environmental and Experimental Botany. - : Elsevier BV. - 0098-8472. ; 56:1, s. 63-71
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Tidskriftsartikel (refereegranskat)abstract
- Field-grown crops of one modem ('Dragon') and one 100-year old ('Lantvete') wheat (Triticum aestivum L.) cultivar were exposed to charcoal-filtered air (CF) or non-filtered air plus additional ozone (NF+) in open-top chambers (n = 6). Ambient air plots (11 = 3) were used to monitor the effects of the chamber enclosure. Quantitative (ear weight, harvest index and 1000-grain weight), as well as qualitative (grain concentration of N. P. K, Ca, Mg, Cd), aspects of crop yield were studied. In addition, the chlorophyll content of the top leaf was followed during the 10-week-long ozone exposure and flag leaf stomatal conductance was monitored. Ear weight was negatively affected by ozone. The effect was smaller in the lower yielding 'Lantvete' compared to the modem cultivar 'Dragon'. A similar ozone effect was found for the harvest index and 1000-grain weight. The difference between cultivars was small for 1000-grain weight, with harvest index significantly lower in 'Lantvete' compared with 'Dragon'. The crude protein concentration of the grain was higher in 'Lantvete', and was enhanced by ozone exposure. No significant treatment or cultivar effects were observed on grain Ca and Cd concentrations, but the greatest chamber effect was on Cd, which was considerably higher in grain from treatment chambers compared with ambient air (possibly due to the higher rate of transpiration in the plants enclosed in the chambers). There were strong differences with respect to grain P, K and Mg concentration between cultivars; 'Lantvete' exhibiting higher concentrations than 'Dragon' in all cases, apart from K. Weak, but significant, increases in grain P, K and Mg concentrations were evident in O-3-treated plants. The chlorophyll concentration of the flag leaf was negatively affected by ozone exposure after approximately I month, but chlorophyll content declined faster in 'Dragon' than 'Lantvete'. Flag leaf chlorophyll concentration was significantly lower in 'Lantvete' compared with 'Dragon' before onset of ozone effects in NF+ and during most of the experiment in CF. Stomatal conductance was also significantly lower in 'Lantvete' than in 'Dragon'. The most important conclusion drawn from the present study is that the 'older' cultivar, 'Lantvete', was less affected by ozone than the modem, bred cultivar, 'Dragon'. This observation might to a large extent be explained by the higher stomatal conductance exhibited by the modern wheat cultivar. The result is consistent with earlier investigations for Greek wheat cultivars, and suggests that the findings reported by others, based on vegetative growth, may extend to grain yield. Growth dilution effects (i.e. the lower observed concentration of an element at higher biomass yield) may explain observed differences between cultivars, and between ozone treatments, in the level of various elements, except for potassium. (c) 2005 Elsevier B.V. All rights reserved.
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