Effects on conformational states of the rabbit sodium/glucose cotransporter through modulation of polarity and charge at glutamine 457

Insights from the molecular docking analysis of SGLT2 and FIMH to combat uropathogenicity

SGLT2 inhibitors are a novel class of FDA approved anti-diabetes drugs. They act by blocking the SGLT2 protein, which prevents glucose reabsorption, leading in enhance glucose excretion and lower blood glucose levels. In diabetic patients, SGLT2 inhibitors have been linked to urinary tract infections (UTIs). Therefore, the development of novel SGLT2 inhibitors with no adverse effects is a need of time. With this purpose, in this study, 48164natural compounds from ZINC database were screened targeting both the SGLT2 and FimH protein using insilico approaches. FimH has been discovered as a promising target for preventing and treating UTIs. The hit compounds ZINC69481892, ZINC1612996, and ZINC4039265 exhibited strong binding with both SGLT2 and FimH with binding energies values of -9.88, -8.96, and -10.57 kcal/mol for SGLT2, and -7.86, -7.01, and -8.92 kcal/mol for FimH, which is higher than that of controls (-6.78 kcal/mol (Empaglifozolin for SGLT2) and -5.14 kcal/mol (Heptyl α-d-mannopyranoside for FimH)). Hits were found to bind with key residues of both SGLT2 and FimH protein. In addition, physiochemical properties showed that these compounds have good drug-likeness properties. Therefore, we anticipate that if these compounds are investigated further, might be potential SGLT2 inhibitors with less uropathogenic adverse effects.

The Molecular Basis of Glucose Galactose Malabsorption in a Large Swedish Pedigree

Glucose-galactose malabsorption (GGM) is due to mutations in the gene coding for the intestinal sodium glucose cotransporter SGLT1 (SLC5A1). Here we identify the rare variant Gln457Arg (Q457R) in a large pedigree of patients in the Västerbotten County in Northern Sweden with the clinical phenotype of GGM. The functional effect of the Q457R mutation was determined in protein expressed in Xenopus laevis oocytes using biophysical and biochemical methods. The mutant failed to transport the specific SGLT1 sugar analog α-methyl-D-glucopyranoside (αMDG). Q457R SGLT1 was synthesized in amounts comparable to the wild-type (WT) transporter. SGLT1 charge measurements and freeze-fracture electron microscopy demonstrated that the mutant protein was inserted into the plasma membrane. Electrophysiological experiments, both steady-state and presteady-state, demonstrated that the mutant bound sugar with an affinity lower than the WT transporter. Together with our previous studies on Q457C and Q457E mutants, we established that the positive charge on Q457R prevented the translocation of sugar from the outward-facing to inward-facing conformation. This is contrary to other GGM cases where missense mutations caused defects in trafficking SGLT1 to the plasma membrane. Thirteen GGM patients are now added to the pedigree traced back to the late 17^th century. The frequency of the Q457R variant in Västerbotten County genomes, 0.0067, is higher than in the general Swedish population, 0.0015, and higher than the general European population, 0.000067. This explains the high number of GGM cases in this region of Sweden.

Biocomputational Prediction Approach Targeting FimH by Natural SGLT2 Inhibitors: A Possible Way to Overcome the Uropathogenic Effect of SGLT2 Inhibitor Drugs

The Food and Drug Administration (FDA) approved a new class of anti-diabetic medication (a sodium-glucose co-transporter 2 (SGLT2) inhibitor) in 2013. However, SGLT2 inhibitor drugs are under evaluation due to their associative side effects, such as urinary tract and genital infection, urinary discomfort, diabetic ketosis, and kidney problems. Even clinicians have difficulty in recommending it to diabetic patients due to the increased probability of urinary tract infection. In our study, we selected natural SGLT2 inhibitors, namely acerogenin B, formononetin, (-)-kurarinone, (+)-pteryxin, and quinidine, to explore their potential against an emerging uropathogenic bacterial therapeutic target, i.e., FimH. FimH plays a critical role in the colonization of uropathogenic bacteria on the urinary tract surface. Thus, FimH antagonists show promising effects against uropathogenic bacterial strains via their targeting of FimH's adherence mechanism with less chance of resistance. The molecular docking results showed that, among natural SGLT2 inhibitors, formononetin, (+)-pteryxin, and quinidine have a strong interaction with FimH proteins, with binding energy (∆G) and inhibition constant (ki) values of -5.65 kcal/mol and 71.95 µM, -5.50 kcal/mol and 92.97 µM, and -5.70 kcal/mol and 66.40 µM, respectively. These interactions were better than those of the positive control heptyl α-d-mannopyranoside and far better than those of the SGLT2 inhibitor drug canagliflozin. Furthermore, a 50 ns molecular dynamics simulation was conducted to optimize the interaction, and the resulting complexes were found to be stable. Physicochemical property assessments predicted little toxicity and good drug-likeness properties for these three compounds. Therefore, formononetin, (+)-pteryxin, and quinidine can be proposed as promising SGLT2 inhibitors drugs, with add-on FimH inhibition potential that might reduce the probability of uropathogenic side effects.

Phospholipid effects on SGLT1-mediated glucose transport in rabbit ileum brush border membrane vesicles

In small intestine, sodium-glucose cotransporter SGLT1 provides the main mechanism for sugar uptake. We investigated the effect of membrane phospholipids (PL) on this transport in rabbit ileal brush border membrane vesicles (BBMV). For this, PL of different charge, length, and saturation were incorporated into BBMV. Transport was measured related to (i) membrane surface charge (membrane-bound MC540 fluorescence), (ii) membrane thickness (PL incorporation of different acyl chain length), and (iii) membrane fluidity (r_12AS, fluorescence anisotropy of 12-AS). Compared to phosphatidylcholine (PC) carrying a neutral head group, inhibition of SGLT1 increased considerably with the acidic phosphatidic acid (PA) and phosphatidylinositol (PI) that increase membrane negative surface charge. The order of PL potency was PI>PA > PE = PS > PC. Inhibition by acidic PA-oleate was 5-times more effective than with neutral PE (phosphatidylethanolamine)-oleate. Lineweaver-Burk plot indicated uncompetitive inhibition of SGLT1 by PA. When membrane thickness was increased by neutral PC of varying acyl chain length, transport was increasingly inhibited by 16:1 PC to 22:1 PC. Even more pronounced inhibition was observed with mono-unsaturated instead of saturated acyl chains which increased membrane fluidity (indicated by decreased r_12AS). In conclusion, sodium-dependent glucose transport of rabbit ileal BBMV is modulated by (i) altered membrane surface charge, (ii) length of acyl chains via membrane thickness, and (iii) saturation of PL acyl chains altering membrane fluidity. Transport was attenuated by charged PL with longer and unsaturated acyl residues. Alterations of PL may provide a principle for attenuating dietary glucose uptake.

Molecular Interaction of Anti-Diabetic Drugs With Acetylcholinesterase and Sodium Glucose Co-Transporter 2

Type 2 Diabetes Mellitus (T2DM) and Alzheimer's disease (AD) are the two disorders which are known to share pertinent pathological and therapeutic links. Sodium glucose co-transporter-2 (SGLT2) and Acetylcholinesterase (AChE) are established inhibition targets for T2DM and AD treatments, respectively. Reports suggest that anti-diabetic drugs could be used for AD treatment also. The present study used molecular docking by Autodock4.2 using our "Click-By-Click"-protocol, Ligplot1.4.3 and "change in accessible surface area (ΔASA)-calculations" to investigate the binding of two investigational anti-diabetic drugs, Ertugliflozin and Sotagliflozin to an established target (SGLT2) and a research target (human brain AChE). Sotagliflozin appeared more promising for SGLT2 as well as AChE-inhibition with reference to ΔG and Ki values in comparison to Ertugliflozin. The ΔG and Ki values for "Sotagliflozin:AChE-binding" were -7.16 kcal/mol and 5.6 μM, respectively while the same were found to be -8.47 kcal/mol and 0.62 μM, respectively for its interaction with SGLT2. Furthermore, "Sotagliflozin:SGLT2-interaction" was subjected to (un)binding simulation analyses by "Molecular-Motion-Algorithms." This information is significant as the exact binding mode, interacting amino acid residues and simulation results for the said interaction have not been described yet. Also no X-ray crystal is available for the same. Finally, the results described herein indicate that Sotagliflozin could have an edge over Ertugliflozin for treatment of Type 2 diabetes. Future design of drugs based on Sotagliflozin scaffolds for treatment of Type 2 and/or Type 3 diabetes are highly recommended. As these drugs are still in late phases of clinical trials, the results described herein appear timely. J. Cell. Biochem. 118: 3855-3865, 2017. © 2017 Wiley Periodicals, Inc.

Sugar binding residue affects apparent Na+ affinity and transport stoichiometry in mouse sodium/glucose cotransporter type 3B

SGLT1 is a sodium/glucose cotransporter that moves two Na(+) ions with each glucose molecule per cycle. SGLT3 proteins belong to the same family and are described as glucose sensors rather than glucose transporters. Thus, human SGLT3 (hSGLT3) does not transport sugar, but extracellular glucose depolarizes the cell in which it is expressed. Mouse SGLT3b (mSGLT3b), although it transports sugar, has low apparent sugar affinity and partially uncoupled stoichiometry compared with SGLT1, suggesting that mSGLT3b is also a sugar sensor. The crystal structure of the Vibrio parahaemolyticus SGLT showed that residue Gln(428) interacts directly with the sugar. The corresponding amino acid in mammalian proteins, 457, is conserved in all SGLT1 proteins as glutamine. In SGLT3 proteins, glutamate is the most common residue at this position, although it is a glycine in mSGLT3b and a serine in rat SGLT3b. To test the contribution of this residue to the function of SGLT3 proteins, we constructed SGLT3b mutants that recapitulate residue 457 in SGLT1 and hSGLT3, glutamine and glutamate, respectively. The presence of glutamine at residue 457 increased the apparent Na(+) and sugar affinities, whereas glutamate decreased the apparent Na(+) affinity. Moreover, glutamate transported more cations per sugar molecule than the wild type protein. We propose a model where cations are released intracellularly without the release of sugar from an intermediate state. This model explains the uncoupled charge:sugar transport phenotype observed in wild type and G457E-mSGLT3b compared with SGLT1 and the sugar-activated cation transport without sugar transport that occurs in hSGLT3.