Crystallization and preliminary crystallographic analysis of human muscle phosphofructokinase, the main regulator of glycolysis

Reversal of insulin resistance by Ficus benghalensis bark in fructose-induced insulin-resistant rats

ETHNOPHARMACOLOGICAL RELEVANCE

Bark of Ficus benghalensis L. (family: Moraceae), commonly known as Banyan is recorded as Nyagrodha in Ayurvedic Pharmacopeia of India to manage burning sensation, obesity, diabetes, bleeding disorders, thirst, skin diseases, wounds, and dysmenorrhoea. However, the effect of F. benghalensis bark over glycolysis, gluconeogenesis, and appetite regulation in insulin-resistant pathogenesis has not been reported yet.

AIM OF THE STUDY

The present study aimed to investigate the effect of hydroalcoholic extract of F. benghalensis bark in gluconeogenesis, glycolysis, and appetite regulation in fructose-induced insulin resistance in experimental rats.

MATERIALS AND METHODS

Male Wister rats were supplemented with fructose in drinking water (10% w/v for 42 days and 20% w/v for next 12 days; a total of 54 days); insulin resistance was confirmed via the elevated area under the curve of the glucose during oral glucose tolerance test after 54 days and was subjected with extract treatment for next 30 days. After 30 days of treatment, animals were fasted to perform oral glucose and insulin tolerance test to estimate glucose and insulin levels. The blood sample was collected for biochemical estimation and the liver homogenate was prepared to estimate hepatic enzymes and enzymatic and non-enzymatic anti-oxidant biomarkers followed by histopathological evaluation. Also, glycogen content was quantified in gastrocnemius muscle and liver homogenates. Further, reported bioactives from the F. benghalensis were retrieved from the ChEBI database and docked against hexokinase, phosphofructokinase, glucose-6-phosphatase, lactate dehydrogenase, and fructose-1,6-biphosphatase to identify the probable lead hits against the enzymes involved in gluconeogenesis.

RESULTS

Treatment with the F. benghalensis bark extract significantly increased the body weight and food intake and significantly decreased fructose supplemented water intake. Further, treatment with extract significantly increased the exogenous glucose clearance and well responded to the exogenous insulin. Further, extract treatment improved lipid metabolism, ameliorated plasma leptin, and multiple enzymatic and non-enzymatic antioxidant biomarkers. Likewise, it also improved gluconeogenesis mediated pathogenesis of non-alcoholic fatty liver injury. Additionally, molecular docking also identified mucusisoflavone A and B as lead hits in downregulating gluconeogenesis.

CONCLUSION

Hydroalcoholic extract of F. benghalensis bark may prevent insulin resistance by downregulating gluconeogenesis and improving the appetite in fructose-induced insulin-resistant rats.

Structures, functions, and mechanisms of filament forming enzymes: a renaissance of enzyme filamentation

Filament formation by non-cytoskeletal enzymes has been known for decades, yet only relatively recently has its wide-spread role in enzyme regulation and biology come to be appreciated. This comprehensive review summarizes what is known for each enzyme confirmed to form filamentous structures in vitro, and for the many that are known only to form large self-assemblies within cells. For some enzymes, studies describing both the in vitro filamentous structures and cellular self-assembly formation are also known and described. Special attention is paid to the detailed structures of each type of enzyme filament, as well as the roles the structures play in enzyme regulation and in biology. Where it is known or hypothesized, the advantages conferred by enzyme filamentation are reviewed. Finally, the similarities, differences, and comparison to the SgrAI endonuclease system are also highlighted.

Methylmercury's chemistry: From the environment to the mammalian brain

Methylmercury is a neurotoxicant that is found in fish and rice. MeHg's toxicity is mediated by blockage of -SH and -SeH groups of proteins. However, the identification of MeHg's targets is elusive. Here we focus on the chemistry of MeHg in the abiotic and biotic environment. The toxicological chemistry of MeHg is complex in metazoans, but at the atomic level it can be explained by exchange reactions of MeHg bound to -S(e)H with another free -S(e)H group (R¹S(e)-HgMe + R²-S(e)H ↔ R¹S(e)H + R²-S(e)-HgMe). This reaction was first studied by professor Rabenstein and here it is referred as the "Rabenstein's Reaction". The absorption, distribution, and excretion of MeHg in the environment and in the body of animals will be dictated by Rabenstein's reactions. The affinity of MeHg by thiol and selenol groups and the exchange of MeHg by Rabenstein's Reaction (which is a diffusion controlled reaction) dictates MeHg's neurotoxicity. However, it is important to emphasize that the MeHg exchange reaction velocity with different types of thiol- and selenol-containing proteins will also depend on protein-specific structural and thermodynamical factors. New experimental approaches and detailed studies about the Rabenstein's reaction between MeHg with low molecular mass thiol (LMM-SH) molecules (cysteine, GSH, acetyl-CoA, lipoate, homocysteine) with abundant high molecular mass thiol (HMM-SH) molecules (albumin, hemoglobin) and HMM-SeH (GPxs, Selenoprotein P, TrxR1-3) are needed. The study of MeHg migration from -S(e)-Hg- bonds to free -S(e)H groups (Rabenstein's Reaction) in pure chemical systems and neural cells (with special emphasis to the LMM-SH and HMM-S(e)H molecules cited above) will be critical to developing realistic constants to be used in silico models that will predict the distribution of MeHg in humans.

Effect of the cancer specific shorter form of human 6-phosphofructo-1-kinase on the metabolism of the yeast Saccharomyces cerevisiae

Background

At first glance, there appears to be a high degree of similarity between the metabolism of yeast (the Crabtree effect) and human cancer cells (the Warburg effect). At the root of both effects is accelerated metabolic flow through glycolysis which leads to overflows of ethanol and lactic acid, respectively. It has been proposed that enhanced glycolytic flow in cancer cells is triggered by the altered kinetic characteristics of the key glycolytic regulatory enzyme 6-phosphofructo-1-kinase (Pfk). Through a posttranslational modification, highly active shorter Pfk-M fragments, which are resistant to feedback inhibition, are formed after the proteolytic cleavage of the C-terminus of the native human Pfk-M. Alternatively, enhanced glycolysis is triggered by optimal growth conditions in the yeast Saccharomyces cerevisiae.

Results

To assess the deregulation of glycolysis in yeast cells, the sfPFKM gene encoding highly active human shorter Pfk-M fragments was introduced into pfk-null S. cerevisiae. No growth of the transformants with the sfPFKM gene was observed on glucose and fructose. Glucose even induced rapid deactivation of Pfk1 activities in such transformants. However, Pfk1 activities of the sfPFKM transformants were detected in maltose medium, but the growth in maltose was possible only after the addition of 10 mM of ethanol to the medium. Ethanol seemed to alleviate the severely unbalanced NADH/NADPH ratio in the sfPFKM cells. However, the transformants carrying modified Pfk-M enzymes grew faster than the transformants with the human native human Pfk-M enzyme in a narrow ecological niche with a low maltose concentration medium that was further improved by additional modifications. Interestingly, periodic extracellular accumulation of phenylacetaldehyde was detected during the growth of the strain with modified Pfk-M but not with the strain encoding the human native enzyme.

Conclusions

Highly active cancer-specific shorter Pfk-M fragments appear to trigger several controlling mechanisms in the primary metabolism of yeast S. cerevisiae cells. These results suggest more complex metabolic regulation is present in S. cerevisiae as free living unicellular eukaryotic organisms in comparison to metazoan human cells. However, increased productivity under broader growth conditions may be achieved if more gene engineering is performed to reduce or omit several controlling mechanisms.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-017-0362-5) contains supplementary material, which is available to authorized users.

Crystal structure of human platelet phosphofructokinase-1 locked in an activated conformation

Phosphofructokinase-1 (Pfk) acts as the main control point of flux through glycolysis. It is involved in complex allosteric regulation and Pfk mutations have been linked to cancer development. Whereas the 3D structure and structural basis of allosteric regulation of prokaryotic Pfk has been studied in great detail, our knowledge about the molecular basis of the allosteric behaviour of the more complex mammalian Pfk is still very limited. To characterize the structural basis of allosteric regulation, the subunit interfaces and the functional consequences of modifications in Tarui's disease and cancer, we analysed the physiological homotetramer of human platelet Pfk at up to 2.67 Å resolution in two crystal forms. The crystallized enzyme is permanently activated by a deletion of the 22 C-terminal residues. Complex structures with ADP and fructose-6-phosphate (F6P) and with ATP suggest a role of three aspartates in the deprotonation of the OH-nucleophile of F6P and in the co-ordination of the catalytic magnesium ion. Changes at the dimer interface, including an asymmetry observed in both crystal forms, are the primary mechanism of allosteric regulation of Pfk by influencing the F6P-binding site. Whereas the nature of this conformational switch appears to be largely conserved in bacterial, yeast and mammalian Pfk, initiation of these changes differs significantly in eukaryotic Pfk.