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The subunit composition of human extracellular superoxide dismutase (EC-SOD) regulates enzymatic activity.

Petersen SV, Valnickova Z, Oury TD, Crapo JD, Chr Nielsen N, Enghild JJ - BMC Biochem. (2007)

Bottom Line: The analyses of EC-SOD purified from human tissue show that all three dimer combinations exist including two homo-dimers (aa and ii) and a hetero-dimer (ai).This finding shows that the aEC-SOD and iEC-SOD subunits combine in all 3 possible ways supporting the presence of tetrameric enzymes with variable enzymatic activity.This variation in enzymatic potency may regulate the antioxidant level in the extracellular space and represent a novel way of modulating enzymatic activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO) Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark. svp@mb.au.dk

ABSTRACT

Background: Human extracellular superoxide dismutase (EC-SOD) is a tetrameric metalloenzyme responsible for the removal of superoxide anions from the extracellular space. We have previously shown that the EC-SOD subunit exists in two distinct folding variants based on differences in the disulfide bridge pattern (Petersen SV, Oury TD, Valnickova Z, Thøgersen IB, Højrup P, Crapo JD, Enghild JJ. Proc Natl Acad Sci USA. 2003;100(24):13875-80). One variant is enzymatically active (aEC-SOD) while the other is inactive (iEC-SOD). The EC-SOD subunits are associated into covalently linked dimers through an inter-subunit disulfide bridge creating the theoretical possibility of 3 dimers (aa, ai or ii) with different antioxidant potentials. We have analyzed the quaternary structure of the endogenous EC-SOD disulfide-linked dimer to investigate if these dimers in fact exist.

Results: The analyses of EC-SOD purified from human tissue show that all three dimer combinations exist including two homo-dimers (aa and ii) and a hetero-dimer (ai). Because EC-SOD is a tetramer the dimers may combine to generate 5 different mature EC-SOD molecules where the specific activity of each molecule is determined by the ratio of aEC-SOD and iEC-SOD subunits.

Conclusion: This finding shows that the aEC-SOD and iEC-SOD subunits combine in all 3 possible ways supporting the presence of tetrameric enzymes with variable enzymatic activity. This variation in enzymatic potency may regulate the antioxidant level in the extracellular space and represent a novel way of modulating enzymatic activity.

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Related in: MedlinePlus

Schematic representing the antioxidant potential of EC-SOD. The EC-SOD subunit exists as an active folding variant with SOD activity (aEC-SOD; filled squares) and an inactive (iEC-SOD; gray circles). Our results show that the two different subunits can combine to form dimers with variable activities. Tetrameric EC-SOD is maintained by interactions within the N-terminal region, which are likely to be unaffected by the folding of the catalytic domain. We thus propose that dimers combine to generate five different tetramers with distinct SOD activities. The relative SOD activity of each structural level is indicated below each structure. The presence or absence of the ECM-binding regions is not indicated, as this is likely not affecting the tetramer assembly.
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Figure 5: Schematic representing the antioxidant potential of EC-SOD. The EC-SOD subunit exists as an active folding variant with SOD activity (aEC-SOD; filled squares) and an inactive (iEC-SOD; gray circles). Our results show that the two different subunits can combine to form dimers with variable activities. Tetrameric EC-SOD is maintained by interactions within the N-terminal region, which are likely to be unaffected by the folding of the catalytic domain. We thus propose that dimers combine to generate five different tetramers with distinct SOD activities. The relative SOD activity of each structural level is indicated below each structure. The presence or absence of the ECM-binding regions is not indicated, as this is likely not affecting the tetramer assembly.

Mentions: Structural considerations suggest that the EC-SOD tetramer is likely to be organized as two interacting dimers [15]. The characterization of the isolated EC-SOD dimer is thus likely to be relevant for the quaternary structure of the intact EC-SOD molecule. We show that the population of authentic EC-SOD molecules purified from human aorta is composed of three different dimers providing evidence for the formation of EC-SOD molecules with variable degrees of enzymatic activity (Figure 5). The purification of the EC-SOD tetramer subclasses is likely to be difficult due to the similar biochemical properties of such molecules. However, it is the N-terminal regions that are responsible for the formation of the EC-SOD tetramers [12] and they are likely not affected by the difference in folding of the catalytic region. It is thus plausible that the identified dimers are able to assemble into tetramers in a random fashion and generate five different EC-SOD tetramers with variable SOD activity as previously hypothesized (see Figure 5) [23].


The subunit composition of human extracellular superoxide dismutase (EC-SOD) regulates enzymatic activity.

Petersen SV, Valnickova Z, Oury TD, Crapo JD, Chr Nielsen N, Enghild JJ - BMC Biochem. (2007)

Schematic representing the antioxidant potential of EC-SOD. The EC-SOD subunit exists as an active folding variant with SOD activity (aEC-SOD; filled squares) and an inactive (iEC-SOD; gray circles). Our results show that the two different subunits can combine to form dimers with variable activities. Tetrameric EC-SOD is maintained by interactions within the N-terminal region, which are likely to be unaffected by the folding of the catalytic domain. We thus propose that dimers combine to generate five different tetramers with distinct SOD activities. The relative SOD activity of each structural level is indicated below each structure. The presence or absence of the ECM-binding regions is not indicated, as this is likely not affecting the tetramer assembly.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2100054&req=5

Figure 5: Schematic representing the antioxidant potential of EC-SOD. The EC-SOD subunit exists as an active folding variant with SOD activity (aEC-SOD; filled squares) and an inactive (iEC-SOD; gray circles). Our results show that the two different subunits can combine to form dimers with variable activities. Tetrameric EC-SOD is maintained by interactions within the N-terminal region, which are likely to be unaffected by the folding of the catalytic domain. We thus propose that dimers combine to generate five different tetramers with distinct SOD activities. The relative SOD activity of each structural level is indicated below each structure. The presence or absence of the ECM-binding regions is not indicated, as this is likely not affecting the tetramer assembly.
Mentions: Structural considerations suggest that the EC-SOD tetramer is likely to be organized as two interacting dimers [15]. The characterization of the isolated EC-SOD dimer is thus likely to be relevant for the quaternary structure of the intact EC-SOD molecule. We show that the population of authentic EC-SOD molecules purified from human aorta is composed of three different dimers providing evidence for the formation of EC-SOD molecules with variable degrees of enzymatic activity (Figure 5). The purification of the EC-SOD tetramer subclasses is likely to be difficult due to the similar biochemical properties of such molecules. However, it is the N-terminal regions that are responsible for the formation of the EC-SOD tetramers [12] and they are likely not affected by the difference in folding of the catalytic region. It is thus plausible that the identified dimers are able to assemble into tetramers in a random fashion and generate five different EC-SOD tetramers with variable SOD activity as previously hypothesized (see Figure 5) [23].

Bottom Line: The analyses of EC-SOD purified from human tissue show that all three dimer combinations exist including two homo-dimers (aa and ii) and a hetero-dimer (ai).This finding shows that the aEC-SOD and iEC-SOD subunits combine in all 3 possible ways supporting the presence of tetrameric enzymes with variable enzymatic activity.This variation in enzymatic potency may regulate the antioxidant level in the extracellular space and represent a novel way of modulating enzymatic activity.

View Article: PubMed Central - HTML - PubMed

Affiliation: Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO) Department of Molecular Biology, Aarhus University, Gustav Wieds Vej 10C, DK-8000 Aarhus C, Denmark. svp@mb.au.dk

ABSTRACT

Background: Human extracellular superoxide dismutase (EC-SOD) is a tetrameric metalloenzyme responsible for the removal of superoxide anions from the extracellular space. We have previously shown that the EC-SOD subunit exists in two distinct folding variants based on differences in the disulfide bridge pattern (Petersen SV, Oury TD, Valnickova Z, Thøgersen IB, Højrup P, Crapo JD, Enghild JJ. Proc Natl Acad Sci USA. 2003;100(24):13875-80). One variant is enzymatically active (aEC-SOD) while the other is inactive (iEC-SOD). The EC-SOD subunits are associated into covalently linked dimers through an inter-subunit disulfide bridge creating the theoretical possibility of 3 dimers (aa, ai or ii) with different antioxidant potentials. We have analyzed the quaternary structure of the endogenous EC-SOD disulfide-linked dimer to investigate if these dimers in fact exist.

Results: The analyses of EC-SOD purified from human tissue show that all three dimer combinations exist including two homo-dimers (aa and ii) and a hetero-dimer (ai). Because EC-SOD is a tetramer the dimers may combine to generate 5 different mature EC-SOD molecules where the specific activity of each molecule is determined by the ratio of aEC-SOD and iEC-SOD subunits.

Conclusion: This finding shows that the aEC-SOD and iEC-SOD subunits combine in all 3 possible ways supporting the presence of tetrameric enzymes with variable enzymatic activity. This variation in enzymatic potency may regulate the antioxidant level in the extracellular space and represent a novel way of modulating enzymatic activity.

Show MeSH
Related in: MedlinePlus