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Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.

ABSTRACT: Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (2). It identified the roles of the (2S)-flavanone and (aS)-HHDP moieties in generating the ECD spectrum of 2 and provided theoretical evidence for the empirical ECD rules applicable to monomeric flavanones and HHDP-containing compounds. The experimentally observed high-amplitude positive Cotton effect (CE) around 240 nm in 2 is derived from the (aS)-HHDP chromophore, while the low-amplitude negative CE in the 260-300 nm region is contributed by both the (aS)-HHDP and (2S)-flavanone moieties. The "linker" glucosyl moiety has little effect on the overall ECD. It appears that the respective chromophores in 2 contribute additively to the overall ECD, and the empirical rules are applicable for configurational assignment. However, if an (aR)-HHDP chromophore is present, as shown in mattucinol-7-O-[4'',6''-O-(aR)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (3), the dominant role of the (aR)-HHDP and interaction between the (aR)-HHDP and (2S)-flavanone moieties in its overall ECD may be confusing when applying the empirical rules to experimental ECD interpretation. Thus, theoretical calculation of the ECD that quantifies the contributions and interactions of different chromophores is essential for the assignment of the absolute configuration of such molecules.

SUBMITTER: Ding Y

PROVIDER: S-EPMC2765519 | biostudies-literature | 2009 Mar

REPOSITORIES: biostudies-literature

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Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.

Ding Yuanqing Y Li Xing-Cong XC Ferreira Daneel D

Journal of natural products 20090301 3

Time-dependent density functional theory (TDDFT) was employed for theoretical calculation of electronic circular dichroism (ECD) of a hexahydroxydiphenoyl (HHDP)-containing flavanone glycoside, mattucinol-7-O-[4'',6''-O-(aS)-hexahydroxydiphenoyl]-beta-d-glucopyranoside (2). It identified the roles of the (2S)-flavanone and (aS)-HHDP moieties in generating the ECD spectrum of 2 and provided theoretical evidence for the empirical ECD rules applicable to monomeric flavanones and HHDP-containing com ...[more]

PMID: 19099470

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Project description:Many chronic diseases, including cancer and neurodegeneration, are linked to proteasome dysregulation. Proteasome activity, essential for maintaining proteostasis in a cell, is controlled by the gating mechanism and its underlying conformational transitions. Thus, developing effective methods to detect gate-related specific proteasome conformations could be a significant contribution to rational drug design. Since the structural analysis suggests that gate opening is associated with a decrease in the content of α-helices and β-sheets and an increase in random coil structures, we decided to explore the application of electronic circular dichroism (ECD) in the UV region to monitor the proteasome gating. A comparison of ECD spectra of wild type yeast 20S proteasome (predominantly closed) and an open-gate mutant (α3ΔN) revealed an increased intensity in the ECD band at 220 nm, which suggests increased contents of random coil and β-turn structures. This observation was further supported by evaluating ECD spectra of human 20S treated with low concentration of SDS, known as a gate-opening reagent. Next, to evaluate the power of ECD to probe a ligand-induced gate status, we treated the proteasome with H2T4, a tetracationic porphyrin that we showed previously to induce large-scale protein conformational changes upon binding to h20S. H2T4 caused a significant increase in the ECD band at 220 nm, interpreted as an induced opening of the 20S gate. In parallel, we imaged the gate-harboring alpha ring of the 20S with AFM, a technique that we used previously to visualize the predominantly closed gate in latent human or yeast 20S and the open gate in α3ΔN mutant. The results were convergent with the ECD data and showed a marked decrease in the content of closed-gate conformation in the H2T4-treated h20S. Our findings provide compelling support for the use of ECD measurements to conveniently monitor proteasome conformational changes related to gating phenomena. We predict that the observed association of spectroscopic and structural results will help with efficient design and characterization of exogenous proteasome regulators.

Dataset Information

Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.

Publications

Theoretical calculation of electronic circular dichroism of a hexahydroxydiphenoyl-containing flavanone glycoside.

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