The conformational flexibility of 5,6,7,8‐tetrahydrobiopterin and 5,6,7,8‐tetrahydroneopterin: a molecular dynamical simulation

Estelberger, Willibald; Mlekusch, Walter; Reibnegger, Gilbert

doi:10.1016/0014-5793(94)01302-h

Cited by 7 publications

(7 citation statements)

References 13 publications

(11 reference statements)

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“…Both families show an almost-cis configuration of the H1‘ and H2‘ protons (Table ), which is consistent with the strong cross-peak observed between these protons in the NOESY spectra. The axial and equatorial conformers of BH 4 in solution may in fact represent real solution conformations due to the conformational flexibility of the cofactor and are in agreement with the results obtained by molecular dynamics (MD) simulations. , In addition, measurements of the 3 J HH in free BH 4 for the H6−H7proS (3.2−3.3 Hz) and H6−H7proR (7.5−8.8 Hz) proton pairs are also indicative of an average conformation between equatorial and axial configuration of the side chain 2 Solution conformation of free BH 4 : expanded region of the NOESY spectrum of BH 4 (5 mM) without enzyme (1 s mixing time, in 100 mM K-phosphate, 200 mM KCl, pH 6.7, 10 mM deuterated DTT, 10% D 2 O at 293 K).…”

Section: Resultssupporting

confidence: 80%

“…Examination of the BH 4 conformation at neutral pH shows that the hydroxyls at the side chain at C6 appear to adopt a cis configuration in solution, and our results are also compatible with both an equatorial and axial orientation of the side chain at C6. 28 Previous results obtained by MD simulations and measurements of the dihedral angles between the H6 proton and the H7proS and H7proR protons by NMR 29,31 have indicated that these two conformers of BH 4 probably coexist in equilibrium at neutral pH. The bioactive bound conformations of BH 4 are, however, compatible with equatorial/ pseudoequatorial and more extended conformations for the chain at C6 (Figure 4).…”

Section: Discussionmentioning

confidence: 81%

“…The axial and equatorial conformers of BH 4 in solution may in fact represent real solution conformations due to the conformational flexibility of the cofactor and are in agreement with the results obtained by molecular dynamics (MD) simulations. 30,31 In addition, measurements of the 3 J HH in free BH 4 for the H6-H7proS (3.2-3.3 Hz) and H6-H7proR (7.5-8.8 Hz) proton pairs are also indicative of an average conformation between equatorial and axial configuration of the side chain. 29 The Enzyme-BH 4 Complexes Studied by NMR.…”

Section: Conformation Of Free Bh 4 In Solution Atmentioning

confidence: 97%

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Tetrahydrobiopterin Binding to Aromatic Amino Acid Hydroxylases. Ligand Recognition and Specificity

et al. 2004

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The three aromatic amino acid hydroxylases (phenylalanine, tyrosine, and tryptophan hydroxylase) and nitric oxide synthase (NOS) all utilize (6R)-l-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)) as cofactor. The pterin binding site in the three hydroxylases is well conserved and different from the binding site in NOS. The structures of phenylalanine hydroxylase (PAH) and of NOS in complex with BH(4) are still the only crystal structures available for the reduced cofactor-enzyme complexes. We have studied the enzyme-bound and free conformations of BH(4) by NMR spectroscopy and molecular docking into the active site of the three hydroxylases, using endothelial NOS as a comparative probe. We have found that the dihydroxypropyl side chain of BH(4) adopts different conformations depending on which hydroxylase it interacts with. All the bound conformations are different from that of BH(4) free in solution at neutral pH. The different bound conformations appear to result from specific interactions with nonconserved amino acids at the BH(4) binding sites of the hydroxylases, notably the stretch 248-251 (numeration in PAH) and the residue corresponding to Ala322 in PAH, i.e., Ser in TH and Ala in TPH. On the basis of analysis of molecular interaction fields, we discuss the selectivity determinants for each hydroxylase and explain the high-affinity inhibitory effect of 7-tetrahydrobiopterin specifically for PAH.

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Section: Resultssupporting

confidence: 80%

Section: Discussionmentioning

confidence: 81%

Section: Conformation Of Free Bh 4 In Solution Atmentioning

confidence: 97%

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Tetrahydrobiopterin Binding to Aromatic Amino Acid Hydroxylases. Ligand Recognition and Specificity

et al. 2004

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“…This suggests a conformational equilibrium of pseudo-equatorial and pseudo-axial conformation of the side chain in position 6 (Fig. 8), in agreement with a molecular dynamics simulation for BH 4 (29,30). DISCUSSION Simon et al (31) and Brown and co-workers (8,18) had proposed an Amadori rearrangement for the remodeling of the ribose moiety by GTP cyclohydrolase, but no direct evidence had been obtained.…”

Section: Resultssupporting

confidence: 68%

Biosynthesis of Pteridines

Bracher

Eisenreich

Schramek

et al. 1998

Journal of Biological Chemistry

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GTP cyclohydrolase I catalyzes a ring expansion affording dihydroneopterin triphosphate from GTP. [1,2,3,4,5-13 C 5 ,2-2 H 1 ]GTP was prepared enzymatically from [U-13 C 6 ]glucose for use as enzyme substrate. Multinuclear NMR experiments showed that the reaction catalyzed by GTP cyclohydrolase I involves the release of a proton from C-2 of GTP that is exchanged with the bulk solvent. Subsequently, a proton is reintroduced stereospecifically from the bulk solvent. This is in line with an Amadori rearrangement mechanism. The proton introduced from solvent occupies the pro-7R position in the enzyme product. The data also confirm that the reaction catalyzed by pyruvoyltetrahydropterin synthase results in the incorporation of solvent protons into positions C-6 and C-3 of the enzyme product. On the other hand, the reaction catalyzed by sepiapterin reductase does not involve any detectable incorporation of solvent protons into tetrahydrobiopterin.Pteridines serve as cofactors for a variety of enzyme-catalyzed reactions. Specifically, tetrahydrofolate (in bacteria and eukaryotic organisms) and tetrahydromethanopterin (in archaea) mediate the transfer of one-carbon fragments, tetrahydrobiopterin (BH 4 ) 1 is implicated in the hydroxylation of aromatic amino acids and the formation of nitric oxide in animals (1, 2), and molybdopterin is required as cofactor by a variety of redox enzymes, e.g. xanthine dehydrogenase. The metabolic roles of these cofactors have been reviewed repeatedly (3-6).The formation of pterins by ring expansion of guanosine, including an Amadori rearrangement of the ribose moiety, was first suggested by Weygand et al. (7) on basis of in vivo studies using 14 C-labeled precursors. Subsequent studies by Brown and Burg (8) and by Shiota et al. (9) showed that the first committed step in the biosynthesis of tetrahydrofolate and BH 4 is catalyzed by the enzyme GTP cyclohydrolase I. More specifically, C-8 of GTP (Fig. 1, compound 1) is released as formate, carbon atoms 1Ј and 2Ј of the ribose moiety are utilized for the formation of the dihydropyrazine ring, and carbon atoms 3Ј-5Ј of GTP afford the position 6 side chain of dihydroneopterin triphosphate (NH 2 TP) (Fig. 1, compound 2) (for a review, see Ref.3).The product of GTP cyclohydrolase I, NH 2 TP, is converted to BH 4 (compound 4) by the consecutive action of pyruvoyltetrahydropterin synthase (PPH 4 synthase) and sepiapterin reductase (10 -12). PPH 4 synthase catalyzes the elimination of triphosphate from NH 2 TP as well as a series of tautomerization reactions that are conducive to the formation of a tetrahydropterin from the dihydropterin substrate. Both carbonyl groups of the resulting pyruvoyltetrahydropterin (PPH 4 , compound 3) are subsequently reduced by the action of sepiapterin reductase.The three-dimensional structures of GTP cyclohydrolase I from Escherichia coli (13, 14), PPH 4 synthase from rat (15, 16), and sepiapterin reductase (17) from mouse have been determined by x-ray crystallography. The folding patterns of GTP cyclohydrolase I ...

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“…In general, conformational analysis of tetrahydropterins using NMR tends to suffer from the difficulties posed by rapid exchange at N 5 and N 8 . The possibility that the conformational flexibility of tetrahydropterins may be limited, and thereby able to affect its reactivity, has been raised , and discounted , in a primarily computational vein.…”

Section: B Solution Studies1 General Propertiesmentioning

confidence: 99%