Quenching of triplet states of aromatic ketones by sulfur-containing amino acids in solution. Evidence for electron transfer

Marciniak, Bronisław; Bobrowski, Krzysztof; Hug, Gordon L.

doi:10.1021/j100148a015

Cited by 98 publications

(87 citation statements)

References 14 publications

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“…This observation led to the confirmation of suspected contact sites in several peptidergic receptors (15,16,35). The Met-selective labeling mechanism of the benzophenone radical is based on the formation of a chargetransfer complex between the photogenerated radical and the sulfur atom in the thioether (20,21). The following step, that is, insertion of the ketone radical into an adjacent C-H bond, can occur either in the ␥-methylene or the ⑀-methyl group, with only the latter leading to ligand release upon CNBr cleavage (Fig.…”

Section: Discussionmentioning

confidence: 94%

“…1A) have been shown to incorporate into Met residues at a disproportionate frequency (13). Previous photochemical studies of the benzophenone radical have indicated that it exhibits strong selectivity for thioether groups (20,21). This selectivity would explain the high ratio of methionine insertion into target proteins through benzophenone photoaffinity labeling.…”

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confidence: 99%

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Determining the Environment of the Ligand Binding Pocket of the Human Angiotensin II Type I (hAT1) Receptor Using the Methionine Proximity Assay

Clement

Martin

Beaulieu

et al. 2005

Journal of Biological Chemistry

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The peptide hormone angiotensin II (AngII) binds to the AT 1 (angiotensin type 1) receptor within the transmembrane domains in an extended conformation, and its C-terminal residue interacts with transmembrane domain VII at Phe-293/Asn-294. The molecular environment of this binding pocket remains to be elucidated. The preferential binding of benzophenone photolabels to methionine residues in the target structure has enabled us to design an experimental approach called the methionine proximity assay, which is based on systematic mutagenesis and photolabeling to determine the molecular environment of this binding pocket. The octapeptide hormone angiotensin II (AngII) 1 (Fig. 1A) is the active component of the renin-angiotensin system. Virtually all known physiological effects of AngII are produced through the activation of the hAT 1 receptor, which belongs to the class A rhodopsin-like family of the heptahelical G proteincoupled receptor (GPCR) superfamily (1, 2). Elucidating the stereochemistry of the ligand-receptor interaction is vital for understanding the mechanism of ligand binding, GPCR activation, and, eventually, rational drug design.In the past, much effort was devoted to identifying the domains or individual residues of a given receptor that may interact with its ligand. Most experiments to address ligandreceptor interactions were performed with series of receptor mutants to identify specific residues critical to ligand binding (3-5). It is, however, speculative to deduce precise structures of ligand-receptor interactions through mutagenesis studies alone. More direct approaches have therefore been used to study ligand-receptor interactions. Among these is photoaffinity labeling, which allows covalent incorporation of the ligand within its binding site, presumably at the contact area of the photolabel in the receptor. This ligand-receptor contact can be identified by specific enzymatic or chemical digestion of the labeled receptor (6) or by mass spectrometry (7). The binding pockets within the transmembrane domains of several bioamine receptors have been identified using this kind of approach. The adenosine A 1 receptor (8) and the ␤ 2 adrenergic receptor (9, 10) are typical examples. Peptidergic receptors such as hAT 1 and hAT 2 (11, 12), neurokinin receptors (13), and several other receptors from the secretin GPCR family B (14) have been also studied using this approach. We previously identified ligandcontact points within the second extracellular loop (ECL) and the seventh transmembrane domain (TMD) of the hAT 1 receptor (12,15,16). Although photoaffinity labeling has been widely used to study peptidergic GPCR binding pockets, generally only a single contact point between a given ligand and its cognate receptor has been identified. The resulting information does not, however, induce sufficient restrictions to generate credible GPCR structures in the ligand-bound state using homology modeling.Labeling studies using benzophenone residues have identified many ligand-receptor contact points with a surpris...

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Section: Discussionmentioning

confidence: 94%

mentioning

confidence: 99%

Determining the Environment of the Ligand Binding Pocket of the Human Angiotensin II Type I (hAT1) Receptor Using the Methionine Proximity Assay

Clement

Martin

Beaulieu

et al. 2005

Journal of Biological Chemistry

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“…Many benzophenone labeling studies have identified Met residues as covalent attachment sites because of the pronounced photochemical selectivity of benzophenone photolabels for Met residue (12,13 (7.44) and Asn-294 (7.45) of TMD VII (21,30), strongly suggesting that no endogenous Met residues are accessible to position 8 of AngII in the hAT 1 binding pocket. Met residues introduced into the hAT 1 receptor by site-directed mutagenesis in a position proximal to the photoreactive moiety of 125 I-[Sar 1 ,Bpa 8 ]AngII should pull toward it part or all of the labeling upon binding and UV irradiation of the ligand receptor complex.…”

Section: Discussionmentioning

confidence: 99%

“…Peptide labels containing the photoreactive amino acid pЈ-benzoyl-L-phenylalanine (Bpa) (Fig. 1) preferentially bond to Met residues because of their strong photochemical selectivity for thioether groups (12,13). This selectivity has been exploited in the methionine proximity assay (MPA) where Met residues are introduced into target structures as bait to identify receptor residues in close proximity to the labeling position of the ligand (14,15) and thus to determine the immediate molecular environment of the receptor in the vicinity of the labeling position.…”

Section: Angiimentioning

confidence: 99%

Activation Induces Structural Changes in the Liganded Angiotensin II Type 1 Receptor

Clement¹,

Cabana

Holleran

et al. 2009

Journal of Biological Chemistry

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“…It is clearly shown that formation of Gly-Met(O 2 )-Gly started from $1200 mV and increased until 2500 mV, after which the signal intensity slightly decreased to a stable range of the voltammogram from 2500 to 3000 mV ( Figure 11(C)). We have shown that generation of OH-radicals occurs at potentials higher than 2000 mV on BDD electrode in this cell, using LFL oxidation as the readout [35]. The formation of Gly-Met(O 2 )-Gly occurred based on further oxidation of Gly-Met(O)-Gly, indicated by the consuming of GlyMet(O)-Gly from 1200 mV to 2500 mV.…”

Section: Electrochemical Oxidation Of Gly-met-glymentioning

confidence: 84%

Radiation chemical studies of Gly-Met-Gly in aqueous solution

Barata‐Vallejo

Ferreri

Zhang

et al. 2016

Free Radical Research

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Important biological consequences are related to the reaction of HO radicals with methionine (Met). Several fundamental aspects remain to be defined when Met is an amino acid residue incorporated in the interior of peptides and proteins. The present study focuses on Gly-Met-Gly, the simplest peptide where Met is not a terminal residue. The reactions of HO with Gly-Met-Gly and its N-acetyl derivative were studied by pulse radiolysis technique. The transient absorption spectra were resolved into contributions from specific components of radical intermediates. Moreover, a detailed product analysis is provided for the first time for Met-containing peptides in radiolytic studies to support the mechanistic proposal. By parallel radiolytical and electrochemical reactions and consequent product identification, the formation of sulfoxide attributed to the direct HO radical attack on the sulfide functionality of the Met residue could be excluded, with the in situ generated hydrogen peroxide responsible for this oxidation. LC-MS and high resolution MS/MS were powerful analytical tools to envisage the structures of five products, thus allowing to complete the mechanistic picture of the overall Met-containing peptide reactivity. ARTICLE HISTORY

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Quenching of triplet states of aromatic ketones by sulfur-containing amino acids in solution. Evidence for electron transfer

Cited by 98 publications

References 14 publications

Determining the Environment of the Ligand Binding Pocket of the Human Angiotensin II Type I (hAT1) Receptor Using the Methionine Proximity Assay

Determining the Environment of the Ligand Binding Pocket of the Human Angiotensin II Type I (hAT1) Receptor Using the Methionine Proximity Assay

Activation Induces Structural Changes in the Liganded Angiotensin II Type 1 Receptor

Radiation chemical studies of Gly-Met-Gly in aqueous solution

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