1rm4
From Proteopedia
(New page: 200px<br /><applet load="1rm4" size="450" color="white" frame="true" align="right" spinBox="true" caption="1rm4, resolution 2.00Å" /> '''Crystal structure of...) |
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| - | [[Image:1rm4.gif|left|200px]]<br /><applet load="1rm4" size=" | + | [[Image:1rm4.gif|left|200px]]<br /><applet load="1rm4" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="1rm4, resolution 2.00Å" /> | caption="1rm4, resolution 2.00Å" /> | ||
'''Crystal structure of recombinant photosynthetic glyceraldehyde-3-phosphate dehydrogenase A4 isoform, complexed with NADP'''<br /> | '''Crystal structure of recombinant photosynthetic glyceraldehyde-3-phosphate dehydrogenase A4 isoform, complexed with NADP'''<br /> | ||
==Overview== | ==Overview== | ||
| - | Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher | + | Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher plants uses both NADP(H) and NAD(H) as coenzyme and consists of one (GapA) or two types of subunits (GapA, GapB). AB-GAPDH is regulated in vivo through the action of thioredoxin and metabolites, showing higher kinetic preference for NADPH in the light than in darkness due to a specific effect on kcat(NADPH). Previous crystallographic studies on spinach chloroplast A4-GAPDH complexed with NADP or NAD showed that residues Thr33 and Ser188 are involved in NADP over NAD selectivity by interacting with the 2'-phosphate group of NADP. This suggested a possible involvement of these residues in the regulatory mechanism. Mutants of recombinant spinach GapA (A4-GAPDH) with Thr33 or Ser188 replaced by Ala (T33A, S188A and double mutant T33A/S188A) were produced, expressed in Escherichia coli, and compared to wild-type recombinant A4-GAPDH, in terms of crystal structures and kinetic properties. Affinity for NADPH was decreased significantly in all mutants, and kcat(NADPH) was lowered in mutants carrying the substitution of Ser188. NADH-dependent activity was unaffected. The decrease of kcat/Km of the NADPH-dependent reaction in Ser188 mutants resembles the behaviour of AB-GAPDH inhibited by oxidized thioredoxin, as confirmed by steady-state kinetic analysis of native enzyme. A significant expansion of size of the A4-tetramer was observed in the S188A mutant compared to wild-type A4. We conclude that in the absence of interactions between Ser188 and the 2'-phosphate group of NADP, the enzyme structure relaxes to a less compact conformation, which negatively affects the complex catalytic cycle of GADPH. A model based on this concept might be developed to explain the in vivo light-regulation of the GAPDH. |
==About this Structure== | ==About this Structure== | ||
| - | 1RM4 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Spinacia_oleracea Spinacia oleracea] with SO4 and NDP as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Glyceraldehyde-3-phosphate_dehydrogenase_(NADP(+))_(phosphorylating) Glyceraldehyde-3-phosphate dehydrogenase (NADP(+)) (phosphorylating)], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.2.1.13 1.2.1.13] Full crystallographic information is available from [http:// | + | 1RM4 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Spinacia_oleracea Spinacia oleracea] with <scene name='pdbligand=SO4:'>SO4</scene> and <scene name='pdbligand=NDP:'>NDP</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Glyceraldehyde-3-phosphate_dehydrogenase_(NADP(+))_(phosphorylating) Glyceraldehyde-3-phosphate dehydrogenase (NADP(+)) (phosphorylating)], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=1.2.1.13 1.2.1.13] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1RM4 OCA]. |
==Reference== | ==Reference== | ||
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[[Category: rossmann fold]] | [[Category: rossmann fold]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 14:52:21 2008'' |
Revision as of 12:52, 21 February 2008
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Crystal structure of recombinant photosynthetic glyceraldehyde-3-phosphate dehydrogenase A4 isoform, complexed with NADP
Overview
Chloroplast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of higher plants uses both NADP(H) and NAD(H) as coenzyme and consists of one (GapA) or two types of subunits (GapA, GapB). AB-GAPDH is regulated in vivo through the action of thioredoxin and metabolites, showing higher kinetic preference for NADPH in the light than in darkness due to a specific effect on kcat(NADPH). Previous crystallographic studies on spinach chloroplast A4-GAPDH complexed with NADP or NAD showed that residues Thr33 and Ser188 are involved in NADP over NAD selectivity by interacting with the 2'-phosphate group of NADP. This suggested a possible involvement of these residues in the regulatory mechanism. Mutants of recombinant spinach GapA (A4-GAPDH) with Thr33 or Ser188 replaced by Ala (T33A, S188A and double mutant T33A/S188A) were produced, expressed in Escherichia coli, and compared to wild-type recombinant A4-GAPDH, in terms of crystal structures and kinetic properties. Affinity for NADPH was decreased significantly in all mutants, and kcat(NADPH) was lowered in mutants carrying the substitution of Ser188. NADH-dependent activity was unaffected. The decrease of kcat/Km of the NADPH-dependent reaction in Ser188 mutants resembles the behaviour of AB-GAPDH inhibited by oxidized thioredoxin, as confirmed by steady-state kinetic analysis of native enzyme. A significant expansion of size of the A4-tetramer was observed in the S188A mutant compared to wild-type A4. We conclude that in the absence of interactions between Ser188 and the 2'-phosphate group of NADP, the enzyme structure relaxes to a less compact conformation, which negatively affects the complex catalytic cycle of GADPH. A model based on this concept might be developed to explain the in vivo light-regulation of the GAPDH.
About this Structure
1RM4 is a Single protein structure of sequence from Spinacia oleracea with and as ligands. Active as Glyceraldehyde-3-phosphate dehydrogenase (NADP(+)) (phosphorylating), with EC number 1.2.1.13 Full crystallographic information is available from OCA.
Reference
Coenzyme site-directed mutants of photosynthetic A4-GAPDH show selectively reduced NADPH-dependent catalysis, similar to regulatory AB-GAPDH inhibited by oxidized thioredoxin., Sparla F, Fermani S, Falini G, Zaffagnini M, Ripamonti A, Sabatino P, Pupillo P, Trost P, J Mol Biol. 2004 Jul 23;340(5):1025-37. PMID:15236965
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