Structural basis of an epitope tagging system derived from Haloarcula marismortui bacteriorhodopsin I D94N and its monoclonal antibody GD-26

Specific antibody interactions with short peptides have made epitope tagging systems a vital tool employed in virtually all fields of biological research. Here, we present a novel epitope tagging system comprised of a monoclonal antibody named GD‐26, which recognises the TD peptide (GTGATPADD) derived from Haloarcula marismortui bacteriorhodopsin I (HmBRI) D94N mutant. The crystal structure of the antigen‐binding fragment (Fab) of GD‐26 complexed with the TD peptide was determined to a resolution of 1.45 Å. The TD peptide was found to adopt a 3₁₀ helix conformation within the binding cleft, providing a characteristic peptide structure for recognition by GD‐26 Fab. Based on the structure information, polar and nonpolar forces collectively contribute to the strong binding. Attempts to engineer the TD peptide show that the proline residue is crucial for the formation of the 3₁₀ helix in order to fit into the binding cleft. Isothermal calorimetry (ITC) reported a dissociation constant K_D of 12 ± 2.8 nm, indicating a strong interaction between the TD peptide and GD‐26 Fab. High specificity of GD‐26 IgG to the TD peptide was demonstrated by western blotting, ELISA and immunofluorescence as only TD‐tagged proteins were detected, suggesting the effectiveness of the GD‐26/TD peptide tagging system. In addition to already‐existing epitope tags such as the FLAG tag and the ALFA tag adopting either extended or α‐helix conformations, the unique 3₁₀ helix conformation of the TD peptide together with the corresponding monoclonal antibody GD‐26 offers a novel tagging option for research.

The effects of zinc supplementation on primary human retinal pigment epithelium

Population-based and interventional studies have shown that elevated zinc levels can reduce the progression to advanced age-related macular degeneration. The objective of this study was to assess whether elevated extracellular zinc has a direct effect on retinal pigment epithelial cells (RPE), by examining the phenotype and molecular characteristics of increased extracellular zinc on human primary RPE cells. Monolayers of human foetal primary RPE cells were grown on culture inserts and maintained in medium supplemented with increasing total concentrations of zinc (0, 75, 100, 125 and 150 μM) for up to 4 weeks. Changes in cell viability and differentiation as well as expression and secretion of proteins were investigated. RPE cells developed a confluent monolayer with cobblestone morphology and transepithelial resistance (TER) >200 Ω*cm² within 4 weeks. There was a zinc concentration-dependent increase in TER and pigmentation, with the largest effects being achieved by the addition of 125 μM zinc to the culture medium, corresponding to 3.4 nM available (free) zinc levels. The cells responded to addition of zinc by significantly increasing the expression of Retinoid Isomerohydrolase (RPE65) gene; cell pigmentation; Premelanosome Protein (PMEL17) immunoreactivity; and secretion of proteins including Apolipoprotein E (APOE), Complement Factor H (CFH), and High-Temperature Requirement A Serine Peptidase 1 (HTRA1) without an effect on cell viability. This study shows that elevated extracellular zinc levels have a significant and direct effect on differentiation and function of the RPE cells in culture, which may explain, at least in part, the positive effects seen in clinical settings. The results also highlight that determining and controlling of available, as opposed to total added, zinc will be essential to be able to compare results obtained in different laboratories.

Zinc-induced self-association of complement C3b and Factor H: implications for inflammation and age-related macular degeneration

The sub-retinal pigment epithelial deposits that are a hallmark of age-related macular degeneration contain both C3b and millimolar levels of zinc. C3 is the central protein of complement, whereas C3u is formed by the spontaneous hydrolysis of the thioester bridge in C3. During activation, C3 is cleaved to form active C3b, then C3b is inactivated by Factor I and Factor H to form the C3c and C3d fragments. The interaction of zinc with C3 was quantified using analytical ultracentrifugation and x-ray scattering. C3, C3u, and C3b associated strongly in >100 μM zinc, whereas C3c and C3d showed weak association. With zinc, C3 forms soluble oligomers, whereas C3u and C3b precipitate. We conclude that the C3, C3u, and C3b association with zinc depended on the relative positions of C3d and C3c in each protein. Computational predictions showed that putative weak zinc binding sites with different capacities exist in all five proteins, in agreement with experiments. Factor H forms large oligomers in >10 μM zinc. In contrast to C3b or Factor H alone, the solubility of the central C3b-Factor H complex was much reduced at 60 μM zinc and even more so at >100 μM zinc. The removal of the C3b-Factor H complex by zinc explains the reduced C3u/C3b inactivation rates by zinc. Zinc-induced precipitation may contribute to the initial development of sub-retinal pigment epithelial deposits in the retina as well as reducing the progression to advanced age-related macular degeneration in higher risk patients.

Some new amide complexes of thorium tetrachloride and N-thiocyanate

The amide complexes [ThCl4L3], where L = CH3CON(CH3)2 (dma), C2H5CON(CH3)2 (dmpa), C2H5CON(C2H5)2 (depa), or (CH3)3CCON(CH3)2 (dmpva), [Th(NCS)4L4], where L = dmpa, depa, dmiba ((CH3)2CHCON(CH3)2), or dmpva, and [Th(NCS)4 (dmpva)3] have been prepared and their ir spectra reported. The observations are discussed in terms of the steric crowding about the thorium atom using a cone-packing model.