scholarly journals Aldosereductase: structure, mechanism of action, biological role and functioning according to normo and hyperglycemia

2020 ◽  
Vol 22 (99) ◽  
pp. 125-142
Author(s):  
Y. M. Makukh ◽  
T. M. Gryvul ◽  
A. Ya. Krasnevich ◽  
D. S. Vignan
Keyword(s):  
Aldose Reductase ◽  
Conformational Changes ◽  
Mechanism Of Action ◽  
Active Site ◽  
Mammalian Cells ◽  
Polyol Pathway ◽  
The Body ◽  
Biological Role ◽  
Binary Complex ◽  
Sorbitol Pathway

The review summarizes the literature on the structure, biological role and mechanism of action of aldose reductase at different blood glucose levels. Aldosereductase is the first enzyme of the sorbitol (polyol) pathway to glucose metabolism. In mammals, it is a monomeric protein with a molecular weight of 32–56 kDa, has 347–370 amino acid remainders. Its secondary structure consists of α-helices and β-bends, which alternate in 8 units. The active site of the enzyme is located at the C-terminus of the β-bend and contains a glutathione-binding domain. The active site of aldose reductase consists of two sites: substrate-binding and catalytic. The first is formed mainly by the residues of hydrophilic amino acids, and the second, by hydrophobic ones. The interaction of the enzyme with a coenzyme causes conformational changes in aldose reductase. It is believed that the enzyme functions according to the principle of an ordered “bi-bi” mechanism, that is, the coenzyme binds first, and the oxidized product is released last. The reduction of aldehydes of aldose reductase includes several stages: the interaction of the enzyme with NADPH and the formation of a binary complex, the acceptance of the substrate and the formation of a ternary complex (enzyme-coenzyme-substrate) and the separation of the alcohol-reaction product and the oxidized coenzyme. According to normoglycemia in mammalian cells via the sorbitol pathway, up to 1–3 % of intracellular glucose is restored. Under these conditions, it reduces the content of toxic and reactive aldehydes such as: 4-hydroxy-trans-2-nonenal, malondialdehyde, glyoxal, acrolein and their conjugates with reduced glutathione and carnosine, which are also toxic. Before being excreted from the body, they are reduced by aldose reductase to non-toxic compounds. Thus, the enzyme is one of the components of the body's antioxidant system. Hyperglycemia, which is most pronounced in diabetes, significantly increases the flow of glucose through the sorbitol pathway. The activation of aldosereductase and sorbitol dehydrogenase causes the use of a significant amount of NADPH, which leads to a decrease in antioxidant protection, and the excessive formation of NADH leads to a violation of the ratio of reduced and oxidized forms, known as “pseudohypoxia”. Metabolites of the sorbitol pathway, which are formed in excessive amounts, get toxic effects on metabolism and cellular structures, in particular: sorbitol, as an osmotically active component, causes lens edema, leads to the formation of cataracts, and fructose, fructose-phosphate and 3-deoxyglucasone underlie the pathogenesis of secondary diabetic complications.

scholarly journals Aldose Reductase Differential Inhibitors in Green Tea

Biomolecules ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1003 ◽  
Author(s):  
Francesco Balestri ◽  
Giulio Poli ◽  
Carlotta Pineschi ◽  
Roberta Moschini ◽  
Mario Cappiello ◽  
...  
Keyword(s):  
Gallic Acid ◽  
Green Tea ◽  
Aldose Reductase ◽  
Active Site ◽  
Inhibitory Action ◽  
Computational Study ◽  
Epigallocatechin Gallate ◽  
Polyol Pathway ◽  
Differential Inhibition ◽  
Tea Extract

Aldose reductase (AKR1B1), the first enzyme in the polyol pathway, is likely involved in the onset of diabetic complications. Differential inhibition of AKR1B1 has been proposed to counteract the damaging effects linked to the activity of the enzyme while preserving its detoxifying ability. Here, we show that epigallocatechin gallate (EGCG), one of the most representative catechins present in green tea, acts as a differential inhibitor of human recombinant AKR1B1. A kinetic analysis of EGCG, and of its components, gallic acid (GA) and epigallocatechin (EGC) as inhibitors of the reduction of L-idose, 4-hydroxy2,3-nonenal (HNE), and 3-glutathionyl l-4-dihydroxynonanal (GSHNE) revealed for the compounds a different model of inhibition toward the different substrates. While EGCG preferentially inhibited L-idose and GSHNE reduction with respect to HNE, gallic acid, which was still active in inhibiting the reduction of the sugar, was less active in inhibiting HNE and GSHNE reduction. EGC was found to be less efficient as an inhibitor of AKR1B1 and devoid of any differential inhibitory action. A computational study defined different interactive modes for the three substrates on the AKR1B1 active site and suggested a rationale for the observed differential inhibition. A chromatographic fractionation of an alcoholic green tea extract revealed that, besides EGCG and GA, other components may exhibit the differential inhibition of AKR1B1.

scholarly journals Structural characterization of the apo form and NADH binary complex of human lactate dehydrogenase

2014 ◽  
Vol 70 (5) ◽  
pp. 1484-1490 ◽  
Author(s):  
Sally Dempster ◽  
Stephen Harper ◽  
John E. Moses ◽  
Ingrid Dreveny
Keyword(s):  
Lactate Dehydrogenase ◽  
Conformational Changes ◽  
Active Site ◽  
Anaerobic Respiration ◽  
Crystal Form ◽  
Binary Complex ◽  
Cofactor Binding ◽  
Key Enzyme ◽  
Crystallization Conditions

Lactate dehydrogenase A (LDH-A) is a key enzyme in anaerobic respiration that is predominantly found in skeletal muscle and catalyses the reversible conversion of pyruvate to lactate in the presence of NADH. LDH-A is overexpressed in many tumours and has therefore emerged as an attractive target for anticancer drug discovery. Crystal structures of human LDH-A in the presence of inhibitors have been described, but currently no structures of the apo or binary NADH-bound forms are available for any mammalian LDH-A. Here, the apo structure of human LDH-A was solved at a resolution of 2.1 Å in space groupP4122. The active-site loop adopts an open conformation and the packing and crystallization conditions suggest that the crystal form is suitable for soaking experiments. The soaking potential was assessed with the cofactor NADH, which yielded a ligand-bound crystal structure in the absence of any inhibitors. The structures show that NADH binding induces small conformational changes in the active-site loop and an adjacent helix. A comparison with other eukaryotic apo LDH structures reveals the conservation of intra-loop interactions. The structures provide novel insight into cofactor binding and provide the foundation for soaking experiments with fragments and inhibitors.

scholarly journals Mechanism of Action of Non-Synonymous Single Nucleotide Variations Associated with α-Carbonic Anhydrase II Deficiency

Molecules ◽  
2019 ◽  
Vol 24 (21) ◽  
pp. 3987 ◽  
Author(s):  
Taremekedzwa Allan Sanyanga ◽  
Bilal Nizami ◽  
Özlem Tastan Bishop
Keyword(s):  
Carbonic Anhydrase ◽  
Mechanism Of Action ◽  
Active Site ◽  
The Body ◽  
Carbonic Anhydrase Ii ◽  
Motif Analysis ◽  
Acid Base Balance ◽  
Compensatory Mechanisms ◽  
Single Nucleotide ◽  
Single Nucleotide Variations

Human carbonic anhydrase II (CA-II) is a Zinc (Zn 2 + ) metalloenzyme responsible for maintenance of acid-base balance within the body through the reversible hydration of CO 2 to produce protons (H + ) and bicarbonate (BCT). Due to its importance, alterations to the amino acid sequence of the protein as a result of single nucleotide variations (nsSNVs) have detrimental effects on homeostasis. Six pathogenic CA-II nsSNVs, K18E, K18Q, H107Y, P236H, P236R and N252D were identified, and variant protein models calculated using homology modeling. The effect of each nsSNV was analyzed using motif analysis, molecular dynamics (MD) simulations, principal component (PCA) and dynamic residue network (DRN) analysis. Motif analysis identified 11 functionally important motifs in CA-II. RMSD data indicated subtle SNV effects, while PCA analysis revealed that the presence of BCT results in greater conformational sampling and free energy in proteins. DRN analysis showed variant allosteric effects, and the average betweenness centrality (BC) calculations identified Glu117 as the most important residue for communication in CA-II. The presence of BCT was associated with a reduction to Glu117 usage in all variants, suggesting implications for Zn 2 + dissociation from the CA-II active site. In addition, reductions to Glu117 usage are associated with increases in the usage of the primary and secondary Zn 2 + ligands; His94, His96, His119 and Asn243 highlighting potential compensatory mechanisms to maintain Zn 2 + within the active site. Compared to traditional MD simulation investigation, DRN analysis provided greater insights into SNV mechanism of action, indicating its importance for the study of missense mutation effects in proteins and, in broader terms, precision medicine related research.

Influence of Ascorbic Acid on the Structure and Function of Alpha-2- macroglobulin: Investigations using Spectroscopic and Thermodynamic Techniques

2020 ◽  
Vol 27 (3) ◽  
pp. 201-209
Author(s):  
Syed Saqib Ali ◽  
Mohammad Khalid Zia ◽  
Tooba Siddiqui ◽  
Haseeb Ahsan ◽  
Fahim Halim Khan
Keyword(s):  
Ascorbic Acid ◽  
Conformational Changes ◽  
Structural Changes ◽  
The Body ◽  
Titration Calorimetry ◽  
Spectroscopic Techniques ◽  
Human Beings ◽  
Plasma Ascorbic Acid ◽  
Dietary Antioxidant ◽  
And Function

Background: Ascorbic acid is a classic dietary antioxidant which plays an important role in the body of human beings. It is commonly found in various foods as well as taken as dietary supplement. Objective: The plasma ascorbic acid concentration may range from low, as in chronic or acute oxidative stress to high if delivered intravenously during cancer treatment. Sheep alpha-2- macroglobulin (α2M), a human α2M homologue is a large tetrameric glycoprotein of 630 kDa with antiproteinase activity, found in sheep’s blood. Methods: In the present study, the interaction of ascorbic acid with alpha-2-macroglobulin was explored in the presence of visible light by utilizing various spectroscopic techniques and isothermal titration calorimetry (ITC). Results: UV-vis and fluorescence spectroscopy suggests the formation of a complex between ascorbic acid and α2M apparent by increased absorbance and decreased fluorescence. Secondary structural changes in the α2M were investigated by CD and FT-IR spectroscopy. Our findings suggest the induction of subtle conformational changes in α2M induced by ascorbic acid. Thermodynamics signatures of ascorbic acid and α2M interaction indicate that the binding is an enthalpy-driven process. Conclusion: It is possible that ascorbic acid binds and compromises antiproteinase activity of α2M by inducing changes in the secondary structure of the protein.

scholarly journals Aldose Reductase and the Polyol Pathway in Schwann Cells: Old and New Problems

2021 ◽  
Vol 22 (3) ◽  
pp. 1031
Author(s):  
Naoko Niimi ◽  
Hideji Yako ◽  
Shizuka Takaku ◽  
Sookja K. Chung ◽  
Kazunori Sango
Keyword(s):  
Schwann Cells ◽  
Aldose Reductase ◽  
Critical Role ◽  
Polyol Pathway ◽  
Glucose Flux ◽  
Rate Limiting ◽  
Deficient Mice ◽  
Excess Glucose ◽  
Shed Light ◽  
Immortalized Schwann Cells

Aldose reductase (AR) is a member of the reduced nicotinamide adenosine dinucleotide phosphate (NADPH)-dependent aldo-keto reductase superfamily. It is also the rate-limiting enzyme of the polyol pathway, catalyzing the conversion of glucose to sorbitol, which is subsequently converted to fructose by sorbitol dehydrogenase. AR is highly expressed by Schwann cells in the peripheral nervous system (PNS). The excess glucose flux through AR of the polyol pathway under hyperglycemic conditions has been suggested to play a critical role in the development and progression of diabetic peripheral neuropathy (DPN). Despite the intensive basic and clinical studies over the past four decades, the significance of AR over-activation as the pathogenic mechanism of DPN remains to be elucidated. Moreover, the expected efficacy of some AR inhibitors in patients with DPN has been unsatisfactory, which prompted us to further investigate and review the understanding of the physiological and pathological roles of AR in the PNS. Particularly, the investigation of AR and the polyol pathway using immortalized Schwann cells established from normal and AR-deficient mice could shed light on the causal relationship between the metabolic abnormalities of Schwann cells and discordance of axon-Schwann cell interplay in DPN, and led to the development of better therapeutic strategies against DPN.

Sign in / Sign up

Export Citation Format

Share Document