Mutations in the Hemoglobin Binding Domain of Band 3 Perturb Cellular Metabolism and Alter the Sickling of SS Erythrocytes

Under oxygenated conditions, 4 glycolytic enzymes that perform the terminal steps of glycolysis (phospho-fructoKinase [PFK], lactate dehydrogenase [LDH], aldolase [ALD] and glygeraldehyde 3 phosphate dehydrogenase [GAPDH]) bind to the cytoplasmic domain of band 3. Under deoxy conditions deoxy hemoglobin (Hb) is bound to band 3 and PFK, LDH, ALD and GAPDH are displaced (Campanella et al. PNAS 102, 2005; Blood 112, 2008). We generated transgenic mice in which the sequence encoding the first 35 amino acids of the wild type human band 3 cytoplasmic domain replaced the endogenous mouse band 3 sequences in the Slc4a1 gene, a mutant line in which human amino acids 12-21 were deleted removing the deoxy Hb binding site (-Hb) and a third line in which amino acids 1-11 were deleted creating a high affinity binding site for deoxyHb (++Hb). Erythrocytes from the mutant lines were insensitive to Oxygen concentration resulting in changes in oxygen dependent deformability and other physical properties compared to the wild type line (Chu et al. Blood 128, 2016, Zheng et al. JBC 294, 2019, Zhou et al. Sci. Adv. 5, 2019). We crossed our humanized band 3 mouse strains to the Townes Sickle Cell Disease (SCD) mouse model, maintaining both the human βA and βS alleles to generate human AA, AS and SS mice homozygous for each of the human band 3 cytoplasmic domain sequences. Using an assay in which SS red cells in phosphate buffer are deoxygenated to 6% oxygen over time (Dunkelberger et al., J. Phys. Chem. B 122, 2018), we observed that -Hb band 3/SS mice showed an accelerated rate of sickle cell formation and a higher percent of sickled cells than wild type band 3/SS mice (p<0.01). Conversely, ++Hb band 3/SS mice showed an inhibition of both the rate of sickling and the precent of sickled cells compared to wild type band 3/SS mice (p<0.05). We hypothesized that the inability of the glycolytic enzymes to reversibly bind to band 3 in the mutant mice were responsible for the differences in sickling. To test this hypothesis, we analyzed a panel of 28 cellular metabolites in 12 mice (6 female, 6 male) of each genotype: wild type band 3/AA, -AS and -SS, -Hb band 3/AA, -AS, -SS and ++Hb/AA, -AS, -SS. The metabolites were quantified by LC-MS/MS using an API 4500 triple quadrupole mass spectrometer (AB Sciex), with chromatographic resolution enabled on a polymeric amino column (apHera by Supelco) under alkaline mobile phase conditions (pH ~9.3). Stable isotope dilution and 8pt calibration curves allowed the absolute quantification of each metabolite. Consistent with the constitutive binding of the terminal glycolytic enzymes to band 3 in -Hb erythrocytes, glycolysis was inhibited after the phosphoenol pyruvate step, as evidenced by significant accumulation of the intermediates at top of the glycolysis pathway, including fructose 1,6 biphosphate (FBP; p<0.01), dihydroxyacetone phosphate/ glyceraldehyde-3-phosphate (G3P; p<0.01), and 3-phosphoglycerate/2-phosphoglycerate (PG; p<0.01). In the ++Hb mutant where the terminal glycolytic enzymes are constitutively displaced from band 3, significantly lower levels of FBP, G3P and PG were observed (p<0.01). The levels of these metabolites in wild type band 3/SS erythrocytes were intermediate between the two mutant strains. We hypothesized that the accumulation of FBP, G3P and PG contributed to the increased rate of sickling in the -Hb band 3/SS mice. To test this, we incubated wild type band 3/SS cells with either FBP or PG. Both intermediates increased the rate of sickle cell formation and percentage of sickled cells in a dose dependent fashion with no alteration in any RBC indices including MCV and osmotic fragility. We next hypothesized that reduction of the levels of glycolytic intermediates would have an antisickling effect. To test this, we incubated wild type band 3/SS cells with 2,3 diphosphoglycerol (DPG), which is a potent inhibitor of glycolysis. We found that DPG treatment led to a dose dependent decrease in the rate of sickle cell formation and percentage of sickled cells, again with no alteration in any RBC indices including MCV and osmotic fragility. We conclude that the accumulation of glycolytic intermediates leads to increased sickle cell formation. We propose that reduction in the levels of glycolytic intermediates either by accelerating the terminal stages of glycolysis or by redirection to the pentose phosphate pathway may offer a means to treat SCD. Disclosures No relevant conflicts of interest to declare.

Electronic and Optical Properties of Atomic-Scale Heterostructure Based on MXene and MN (M = Al, Ga): A DFT Investigation

After the discovery of graphene, a lot of research has been conducted on two-dimensional (2D) materials. In order to increase the performance of 2D materials and expand their applications, two different layered materials are usually combined by van der Waals (vdW) interactions to form a heterostructure. In this work, based on first-principles calculation, some charming properties of the heterostructure constructed by Hf2CO2, AlN and GaN are addressed. The results show that Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures can keep their original band structure shape and have strong thermal stability at 300 K. In addition, the Hf2CO2/MN heterostructure has I-type band alignment structure, which can be used as a promising light-emitting device material. The charge transfer between the Hf2CO2 and AlN (or GaN) monolayers is 0.1513 (or 0.0414) |e|. The potential of Hf2CO2/AlN and Hf2CO2/GaN vdW heterostructures decreases by 6.445 eV and 3.752 eV, respectively, across the interface. Furthermore, both Hf2CO2/AlN and Hf2CO2/GaN heterostructures have remarkable optical absorption capacity, which further shows the application prospect of the Hf2CO2/MN heterostructure. The study of this work provides theoretical guidance for the design of heterostructures for use as photocatalytic and photovoltaic devices.

The Potential of X-ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers

In the current manuscript we assess to what extent X-ray photoelectron spectroscopy (XPS) is a suitable tool for probing the dipoles formed at interfaces between self-assembled monolayers and metal substrates. To that aim, we perform dispersion-corrected, slab-type band-structure calculations on a number of biphenyl-based systems bonded to an Au(111) surface via different docking groups. In addition to changing the docking chemistry (and the associated interface dipoles), the impacts of polar tail group substituents and varying dipole densities are also investigated. We find that for densely packed monolayers the shifts of the peak positions of the simulated XP spectra are a direct measure for the interface dipoles. In the absence of polar tail group substituents they also directly correlate with adsorption-induced work function changes. At reduced dipole densities this correlation deteriorates, as work function measurements probe the difference between the Fermi level of the substrate and the electrostatic energy far above the interface, while core level shifts are determined by the local electrostatic energy in the region of the atom from which the photoelectron is excited.

X-Ray Photoelectron Spectroscopy for Determining Interface Dipoles of Self-Assembled Monolayers

In the current manuscript we assess to what extent X-ray photoelectron spectroscopy is a suitable tool for probing the dipoles formed at interfaces between self-assembled monolayers and metal substrates. To that aim, we perform dispersion-corrected, slab-type band-structure calculations on a number of biphenyl-based systems bonded to a Au(111) surface via different docking groups. In addition to changing the docking chemistry (and the associated interface dipoles), also the impacts of polar tail-group substituents and varying dipole densities are investigated. We find that for densely-packed monolayers the shifts of the peak positions of the simulated XP-spectra are a direct measure for the interface dipoles. In the absence of polar tail-group substituents they also directly correlate with adsorption-induced work-function changes. At reduced dipole-densities this correlation deteriorates, as work function measurements probe the difference between the Fermi-level of the substrate and the electrostatic energy far above the interface, while core level shifts are determined by the local electrostatic energy in the region of the atom from which the photoelectron is excited.

Flexural band gaps and response attenuation of periodic piping systems enhanced with localized and distributed resonators

Novel metamaterial concepts can be used to economically reduce flexural vibrations in coupled pipe-rack systems. Here, we model pipe on flexible supports as periodic systems and formulate dispersion relations using Floquet-Bloch theory which is verified by a finite element model. Owing to the flexibility of the coupled system, a narrow pass band is created in low frequency regime, in contrast to the case of pipe without any rack. Two types of vibration reduction mechanisms are investigated for pipe with different supports, i.e. simple and elastic support. In order to tune the band gap behaviour, lateral localized resonators are attached at the centre of each unit cell; conversely, the lateral distributed resonators are realized with a secondary pipe existing in the system. The results reveal that both Bragg and resonance type band gaps coexist in piping systems due to the presence of spatial periodicity and local resonance. Although, the response attenuation of a coupled pipe-rack system with distributed resonators is found to be little lower than the case with the localized one, the relatively low stiffness and damping values lead to cheaper solutions. Therefore, the proposed concept of distributed resonators represents a promising application in piping, power and process industries.

Gigantic work function in layered AgF2

The calculated work function of a powerful oxidizer, AgF2, is 7.76 eV, thus exceeds even that of fluorinated diamond. This unusual property could be used for fabrication of novel junction electronic devices showing ‘‘broken-gap’’ type band alignment.