The backbone and tryptophan side-chain dynamics of both the reduced and oxidized forms of uniformly 15N-labeled Escherichia coli thioredoxin have been characterized using inverse-detected two-dimensional 1H-15N NMR spectroscopy. Longitudinal (T1) and transverse (T2) 15N relaxation time constants and steady-state (1H)-15N NOEs were measured for more than 90% of the protonated backbone nitrogen atoms and for the protonated indole nitrogen atoms of the two tryptophan residues. These data were analyzed by using a model free dynamics formalism to determine the generalized order parameter (S2), the effective correlation time for internal motions (tau e), and 15N exchange broadening contributions (Rex) for each residue, as well as the overall molecular rotational correlation time (tau m). The reduced and oxidized forms exhibit almost identical dynamic behavior on the picosecond to nanosecond time scale. The W31 side chain is significantly more mobile than the W28 side chain, consistent with the positions of W31 on the protein surface and W28 buried in the hydrophobic core. Backbone regions which are significantly more mobile than the average include the N-terminus, which is constrained in the crystal structure of oxidized thioredoxin by specific contacts with a Cu2+ ion, the C-terminus, residues 20-22, which constitute a linker region between the first alpha-helix and the second beta-strand, and residues 73-75 and 93-94, which are located adjacent to the active site. In contrast, on the microsecond to millisecond time scale, reduced thioredoxin exhibits considerable dynamic mobility in the residue 73-75 region, while oxidized thioredoxin exhibits no significant mobility in this region. The possible functional implications of the dynamics results are discussed.

Thiamin-dependent enzymes play key roles in sugar metabolism, typically catalyzing the decarboxylation of ␣-keto acids and the transfer of an aldehyde or an acyl group (1-5). Examples include the E1 components in pyruvate dehydrogenase complexes (PDHc), 2 pyruvate decarboxylase, transketolase, etc. Crystallographic studies (6 -12) have elucidated many of the structural, stereochemical, and biochemical details in the mechanism of action of these enzymes and in the catalytic role of the cofactor ThDP (thiamin diphosphate, vitamin B1 diphosphate, Fig. 1, top left). Despite the enormous contributions made by these and other studies to our understanding of how such enzymes function, important details still remain obscure. There are, for example, no detailed structural data on the first ThDP-bound intermediate in the presence of any enzyme (for example, ␣-lactylthiamin diphosphate (␣-LThDP) in PDHc E1 and pyruvate decarboxylase), which is postulated to form in the currently accepted mechanism of thiamin catalysis (Fig. 1, top, third object from the right). In an effort to obtain structural information pertaining to this key intermediate, we have determined the crystal structure of PDHc E1 from Escherichia coli in complex with ␣-phosphonolactylthiamin diphosphate (PLThDP).PLThDP is the product of the reaction between ThDP and methylacetylphosphonate, with the latter being an analogue of the true substrate pyruvate and a potent inhibitor of PDHc. The complex formed with PLThDP instead of ThDP therefore mimics the structure of the enzyme-bound, reactive tetrahedral intermediate ␣-LThDP (13) in the decarboxylation step of the PDHc E1 reaction. It differs from the complex formed with the true substrate only in the replacement of the carboxylate group by a methyl phosphonate (PO 3 Me) group. However, unlike the C2␣-CO 2 bond normally cleaved in the reaction with pyruvate, the C2␣-PO 3 Me bond remains intact. The reaction is therefore trapped in a pre-CO 2 release-like state, and the structure represents a covalently bound, pre-decarboxylation reaction intermediate analogue.There have been three covalently bound reaction intermediate structures reported for ThDP-dependent enzymes (11,12,14), but they all represented the planar enamine intermediate (Fig. 1, top right object) that exists only after decarboxylation. The E1-PLThDP structure is thus the first structural example of a covalently bound, pre-decarboxylation reaction intermediate analogue in any ThDP-dependent enzyme.* This work was supported by a grant from the Veterans Affairs Merit Review Program and National Institutes of Health Grant GM-61791 (to W. F.) and by National Institutes of Health Grant GM-62330 (to F. J.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. The atomic coordinates and structure factors (codes 2G25 and 2G28)

The crystal structure of the recombinant thiamin diphosphate-dependent E1 component from the Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc) has been determined at a resolution of 1.85 A. The E. coli PDHc E1 component E1p is a homodimeric enzyme and crystallizes with an intact dimer in an asymmetric unit. Each E1p subunit consists of three domains: N-terminal, middle, and C-terminal, with all having alpha/beta folds. The functional dimer contains two catalytic centers located at the interface between subunits. The ThDP cofactors are bound in the "V" conformation in clefts between the two subunits (binding involves the N-terminal and middle domains), and there is a common ThDP binding fold. The cofactors are completely buried, as only the C2 atoms are accessible from solution through the active site clefts. Significant structural differences are observed between individual domains of E1p relative to heterotetrameric multienzyme complex E1 components operating on branched chain substrates. These differences may be responsible for reported alternative E1p binding modes to E2 components within the respective complexes. This paper represents the first structural example of a functional pyruvate dehydrogenase E1p component from any species. It also provides the first representative example for the entire family of homodimeric (alpha2) E1 multienzyme complex components, and should serve as a model for this class of enzymes.

Context:Stress is a state of mental or emotional strain or tension, which can lead to underperformance and adverse clinical conditions. Adaptogens are herbs that help in combating stress. Ayurvedic classical texts, animal studies and clinical studies describe Ashwagandha as a safe and effective adaptogen.Aims:The aim of the study was to evaluate the safety and efficacy of a high-concentration full-spectrum extract of Ashwagandha roots in reducing stress and anxiety and in improving the general well-being of adults who were under stress.Settings and Design:Single center, prospective, double-blind, randomized, placebo-controlled trial.Materials and Methods:A total of 64 subjects with a history of chronic stress were enrolled into the study after performing relevant clinical examinations and laboratory tests. These included a measurement of serum cortisol, and assessing their scores on standard stress-assessment questionnaires. They were randomized to either the placebo control group or the study drug treatment group, and were asked to take one capsule twice a day for a period of 60 days. In the study drug treatment group, each capsule contained 300 mg of high-concentration full-spectrum extract from the root of the Ashwagandha plant. During the treatment period (on Day 15, Day 30 and Day 45), a follow-up telephone call was made to all subjects to check for treatment compliance and to note any adverse reactions. Final safety and efficacy assessments were done on Day 60.Statistical Analysis:t-test, Mann-Whitney test.Results:The treatment group that was given the high-concentration full-spectrum Ashwagandha root extract exhibited a significant reduction (P<0.0001) in scores on all the stress-assessment scales on Day 60, relative to the placebo group. The serum cortisol levels were substantially reduced (P=0.0006) in the Ashwagandha group, relative to the placebo group. The adverse effects were mild in nature and were comparable in both the groups. No serious adverse events were reported.Conclusion:The findings of this study suggest that a high-concentration full-spectrum Ashwagandha root extract safely and effectively improves an individual's resistance towards stress and thereby improves self-assessed quality of life.

The binding of coenzyme and substrate are considered in relation to the known primary and tertiary structure of lactate dehydrogenase (EC 1,1.1.27). The adenine binds in a hydrophobic crevice, and the two coenzyme phosphates are oriented by interactions with the protein. The positively charged guanidinium group of arginine 101 then folds over the negatively charged phosphates, collapsing the loop region overtthe active center and positioning. the ulreactive B side of the nicoti namide in a hydrophobic protein environment. Collapse of the loop also introduces various charged groups into the vicinity of the substrate binding site. The substrate is situated between histidine 195 and the C4 position on the nicotiriamide ring, and is partially oriented by interactions between its carboxyl group and arginine 171. The spatial arrangements of these groups may provide the specificity for the L-isomer of lactate.In this paper coenzyme and substrate binding to dogfish (Squalus acanthius) M4 lactate dehydrogenase (LDH; EC 1.1.1.27) will be discussed in relation to the known amino-acid sequence, the crystal structure determinations, and the effect of various chemical modifications of the enzyme and coenzyme. A comparison of the preliminary 3.0-A resolution structure of the abortive LDH: NAD-pyruvate ternary complex (1) with the more complete 2.0-A resolution structure of the apoenzyme provides information on possible conformational changes during catalysis. Everse and Kaplan (4) have recently reviewed many of the properties of LDH. Evidence from kinetic data indicates that there is an obligatory binding order of coenzyme followed by substrate (Fig. 1), at least near neutral pH (6-8). McPherson (9) has presented evidence to show that the adenine moiety of the coenzyme is required for binding of the nicotinamide moiety.Coenzyme binding Studies on the conformations of adenosine, AMP, and ADP at 2.8-A resolution and of NAD+ at 5.0-resolution, when diffused into crystals of the apoenzyme, are discussed by Chandrasekhar et al. (10). Diffraction patterns of the NADH binary complex closely resemble those of the NAD+ binary complex. Although the structure of each of these binary complexes differs slightly from the other, as a class, their mode of binding of the coenzyme to the apoenzyme is distinct from that of the coenzyme in the ternary complex (Fig. 2). Fig. 3 demonstrates this by a comparison of the structure of NAD in the ternary complex (in black) with (a) NAD+ and (b) AMP in binary complexes. The protein conformation of the apoenzyme differs markedly from that of the ternary complex structure in that the loop (residues 98-114) has folded down over the active center pocket in the ternary complexes. Many smaller conformational changes within the protein are associated with the large movement of the loop and the different position and conformation of the coenzyme.The adenosine binds in a hydrophobic crevice lined by valine 27, glycine 28, an alanine, glycine and valine in the region 29-33, valine 52, valine 54, methionin...

Thiamin thiazolone diphosphate (ThTDP), a potent inhibitor of the E1 component from the Escherichia coli pyruvate dehydrogenase multienzyme complex (PDHc), binds to the enzyme with greater affinity than does the cofactor thiamin diphosphate (ThDP). To identify what determines this difference, the crystal structure of the apo PDHc E1 component complex with ThTDP and Mg(2+) has been determined at 2.1 A and compared to the known structure of the native holoenzyme, PDHc E1-ThDP-Mg(2+) complex. When ThTDP replaces ThDP, reorganization occurs in the protein structure in the vicinity of the active site involving positional and conformational changes in some amino acid residues, a change in the V coenzyme conformation, addition of new hydration sites, and elimination of others. These changes culminate in an increase in the number of hydrogen bonds to the protein, explaining the greater affinity of the apoenzyme for ThTDP. The observed hydrogen bonding pattern is not an invariant feature of ThDP-dependent enzymes but rather specific to this enzyme since the extra hydrogen bonds are made with nonconserved residues. Accordingly, these sequence-related hydrogen bonding differences likewise explain the wide variation in the affinities of different thiamin-dependent enzymes for ThTDP and ThDP. The sequence of each enzyme determines its ability to form hydrogen bonds to the inhibitor or cofactor. Mechanistic roles are suggested for the aforementioned reorganization and its reversal in PDHc E1 catalysis: to promote substrate binding and product release. This study also provides additional insight into the role of water in enzyme inhibition and catalysis.

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Background: The E. coli pyruvate dehydrogenase complex catalyzes conversion of pyruvate to acetyl-CoA and comprises E1p, E2p, and E3 components. Results: The structure of the E2 core domain was solved and shown to efficiently catalyze acetyl transfer between domains. Conclusion: Mass spectrometry revealed hitherto unrecognized domain-induced interactions between E1 and E2 core domain. Significance: A multifaceted approach is required to understand communication between intact multidomain components.