Metal ion-induced permeability changes in cell membranes: A minireview

1994 ◽  
Vol 14 (6) ◽  
pp. 781-789 ◽  
Author(s):  
Tibor Kiss ◽  
Oleg Osipenko
Keyword(s):  
Metal Ion ◽  
Cell Membranes ◽  
Permeability Changes

scholarly journals Electron relay via diffusible and protein-bound flavin cofactor in human six-transmembrane epithelial antigen of the prostate (STEAP)

2021 ◽  
Author(s):  
Gang Wu ◽  
Ming Zhou ◽  
Kehan Chen ◽  
Lie Wang ◽  
Jiemin Shen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Metal Ion ◽  
Time Course ◽  
Cell Membranes ◽  
Structural Changes ◽  
Transmembrane Domain ◽  
Inflammatory Responses ◽  
Electron Flow ◽  
Electron Transfer Chain ◽  
Transfer Chain

Six transmembrane epithelial antigen of the prostate (STEAP) is a family of membrane-embedded metal ion reductases that transfer electrons across the cell membranes. STEAPs are unique to mammals and implicated in metabolic and inflammatory responses and are significantly upregulated in many types of cancer cells. There are four members in the family, STEAP1 - 4, and all STEAPs have a transmembrane domain (TMD) that has a conserved heme binding site, and STEAP2 - 4, but not STEAP1, have an intracellular reductase domain (RED) that binds to NADPH and FAD. NADPH, FAD, and heme form an electron transfer chain that allows electron flow across the cell membranes, however, the mechanism of the stepwise cross-membrane electron transfer remains unclear. It is also unclear how STEAP1, which does not have a RED, acquires and transfers electrons. We expressed and purified human STEAP2 (hSTEAP2), and constructed the electron transfer chain in vitro. Purified hSTEAP2 mediates electron transfer from NADPH to FAD and to heme, with a NADPH oxidation rate of 0.0026 per second. The time course for reduction of heme is more complex with an initial rate of ~ 0.00016 per second. We also found that the heme in hSTEAP2 has a low-spin electron structure and thus a rigid coordination, which is consistent with its high occupancy in the purified protein and its role as part of the electron transfer chain. We then determined the structure of hSTEAP2 in complex with NADP, FAD, and heme by cryo-electron microscopy to 3.2 Å. Human STEAP2 forms a homotrimer and its structure is similar to that of hSTEAP4. NADP+, FAD, and heme are well-resolved in the structure, and while the current conformation would allow electron transfer from FAD to heme, the FAD isoalloxazine ring is ~ 19 Å away from NADPH and does not support hydride transfer. Significant structural changes are required to accommodate dissociation of the FAD isoalloxazine ring from the TMD such that the FAD may become diffusible after its reduction. To test this hypothesis and also to find out how STEAP1 may transfer electrons, we reconstructed an electron transfer chain for STEAP1 and found that the heme in STEAP1 can be reduced by FAD produced either by the full-length STEAP2 or by the soluble RED domain from STEAP4. These results support a diffusible FAD mechanism and demonstrate that STEAP1 is capable of mediating electron transfer across the cell membranes. In summary, our study established a structural and functional framework for further analyses for resolving the mechanism of electron transfer in STEAPs.

scholarly journals Cu and Pb accumulation by the marine diatom Thalassiosira weissflogii in the presence of humic acids

2010 ◽  
Vol 7 (3) ◽  
pp. 309 ◽  
Author(s):  
Paula Sánchez-Marín ◽  
Vera I. Slaveykova ◽  
Ricardo Beiras
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Humic Acids ◽  
Metal Ion ◽  
Cell Membranes ◽  
Marine Diatom ◽  
Membrane Properties ◽  
Thalassiosira Weissflogii ◽  
Cell Surfaces ◽  
Free Metal

Environmental context.Dissolved organic matter protects aquatic microorganisms from toxic metals by complexing and decreasing the concentration of the biologically reactive species such as free metal ions. However, there are some cases of enhancement of toxic effects when humic acids are present, which is thought to be due to effects of adsorbed humic acids on cell membranes. For a marine diatom, humic acids adsorbed to cell surfaces enhanced metal adsorption, whereas intracellular metal contents decreased as a result of metal binding by humic acids. These findings suggest that the diatom wall, the frustule, presents a barrier against direct effects of adsorbed humic acids on the plasma membrane. Abstract.Metal complexation by dissolved organic matter, as humic acids, is considered to decrease metal bioavailability by lowering the free metal ion concentration. However, dissolved organic matter adsorption on cell surfaces can modify cell membrane properties, which can also influence metal uptake. Copper and lead accumulation and internalisation by the marine diatom Thalassiosira weissflogii were studied in the absence and presence of humic acids, and adsorption of humic acids to cell surfaces was evaluated. Both Pb and Cu intracellular concentrations decreased in the presence of humic acids according to labile metal concentrations measured by anodic stripping voltammetry, whereas total (intracellular plus adsorbed) metal content was enhanced in the presence of humic acids, probably owing to enhanced metal plus humics adsorption to cell surfaces. The results of the present work stress the importance of differentiating between intracellular and total cellular metal in bioavailability studies, and suggest that the silica frustule of diatoms represents a barrier against humic acids effects on cell membranes.

Cytolytic peptides induce biphasic permeability changes in mammalian cell membranes

2001 ◽  
Vol 252 (1-2) ◽  
pp. 63-71 ◽  
Author(s):  
Mei Su ◽  
Chufa He ◽  
Charles A West ◽  
Steven J Mentzer
Keyword(s):  
Mammalian Cell ◽  
Cell Membranes ◽  
Permeability Changes ◽  
Cytolytic Peptides

Photoreceptor disk membrane substructures by means of the complementary freeze-fracture-replica methods

1978 ◽  
Vol 36 (2) ◽  
pp. 156-157
Author(s):  
A. Tonosaki ◽  
M. Yamasaki ◽  
H. Washioka ◽  
J. Mizoguchi
Keyword(s):  
Cell Membranes ◽  
Freeze Fracture ◽  
Purple Membrane ◽  
Remarkable Case ◽  
Single Face ◽  
Disk Membrane ◽  
Associated Proteins ◽  
Photoreceptor Membranes

A vertebrate disk membrane is composed of 40 % lipids and 60 % proteins. Its fracture faces have been classed into the plasmic (PF) and exoplasmic faces (EF), complementary with each other, like those of most other types of cell membranes. The hypothesis assuming the PF particles as representing membrane-associated proteins has been challenged by serious questions if they in fact emerge from the crystalline formation or decoration effects during freezing and shadowing processes. This problem seems to be yet unanswered, despite the remarkable case of the purple membrane of Halobacterium, partly because most observations have been made on the replicas from a single face of specimen, and partly because, in the case of photoreceptor membranes, the conformation of a rhodopsin and its relatives remains yet uncertain. The former defect seems to be partially fulfilled with complementary replica methods.

Introduction to Cell Membranes at Molecular Resolution

1978 ◽  
Vol 36 (3) ◽  
pp. 497-502
Author(s):  
R.J. Barrnett
Keyword(s):  
Cell Membranes ◽  
International Federation ◽  
Mountain Range ◽  
Cellular Membranes ◽  
Short History ◽  
Biological Organization ◽  
Macromolecular Assemblies ◽  
The Past

This subject, is like observing the panorama of a mountain range, magnificent towering peaks, but it doesn't take much duration of observation to recognize that they are still in the process of formation. The mountains consist of approaches, materials and methods and the rocky substance of information has accumulated to such a degree that I find myself concentrating on the foothills in the foreground in order to keep up with the advance; the edifices behind form a wonderous, substantive background. It's a short history for such an accumulation and much of it has been moved by the members of the societies that make up this International Federation. My panel of speakers are here to provide what we hope is an interesting scientific fare, based on the fact that there is a continuum of biological organization from biochemical molecules through macromolecular assemblies and cellular membranes to the cell itself. Indeed, this fact explains the whole range of towering peaks that have emerged progressively during the past 25 years.

Aspects of high-resolution imaging with a scanning ion microprobe

1986 ◽  
Vol 44 ◽  
pp. 750-751
Author(s):  
R. Levi-Setti ◽  
J. M. Chabala ◽  
Y. L. Wang
Keyword(s):  
Metal Ion ◽  
Secondary Ion Mass Spectrometry ◽  
Chromatic Aberration ◽  
Ion Source ◽  
Ion Microprobe ◽  
Emission Pattern ◽  
Intrinsic Resolution ◽  
Resolution Imaging ◽  
20 Nm ◽  
Secondary Ion

We have shown the feasibility of 20 nm lateral resolution in both topographic and elemental imaging using probes of this size from a liquid metal ion source (LMIS) scanning ion microprobe (SIM). This performance, which approaches the intrinsic resolution limits of secondary ion mass spectrometry (SIMS), was attained by limiting the size of the beam defining aperture (5μm) to subtend a semiangle at the source of 0.16 mr. The ensuing probe current, in our chromatic-aberration limited optical system, was 1.6 pA with Ga+ or In+ sources. Although unique applications of such low current probes have been demonstrated,) the stringent alignment requirements which they imposed made their routine use impractical. For instance, the occasional tendency of the LMIS to shift its emission pattern caused severe misalignment problems.

Scanning ion microscopy images

1987 ◽  
Vol 45 ◽  
pp. 180-181
Author(s):  
R. Levi-Setti ◽  
J.M. Chabala ◽  
Y.L. Wang
Keyword(s):  
Metal Ion ◽  
Secondary Emission ◽  
Scanning Method ◽  
Ion Channeling ◽  
Secondary Ions ◽  
High Resolution Images ◽  
Ion Microscopy ◽  
Z Contrast ◽  
Focused Beams ◽  
Microscopy Images

Finely focused beams extracted from liquid metal ion sources (LMIS) provide a wealth of secondary signals which can be exploited to create high resolution images by the scanning method. The images of scanning ion microscopy (SIM) encompass a variety of contrast mechanisms which we classify into two broad categories: a) Emission contrast and b) Analytical contrast.Emission contrast refers to those mechanisms inherent to the emission of secondaries by solids under ion bombardment. The contrast-carrying signals consist of ion-induced secondary electrons (ISE) and secondary ions (ISI). Both signals exhibit i) topographic emission contrast due to the existence of differential geometric emission and collection effects, ii) crystallographic emission contrast, due to primary ion channeling phenomena and differential oxidation of crystalline surfaces, iii) chemical emission or Z-contrast, related to the dependence of the secondary emission yields on the Z and surface chemical state of the target.

Freeze-etch TEM of aqueous polymer gel network morphology

1986 ◽  
Vol 44 ◽  
pp. 796-797
Author(s):  
J. A. N. Zasadzinski ◽  
R. K. Prud'homme
Keyword(s):  
Metal Ion ◽  
Polymer Network ◽  
Polymer Gels ◽  
Polymer Gel ◽  
Deformation History ◽  
Crosslinked Polymer ◽  
Aqueous Polymer ◽  
History Of ◽  
Gel Network ◽  
Network Morphology

The rheological and mechanical properties of crosslinked polymer gels arise from the structure of the gel network. In turn, the structure of the gel network results from: thermodynamically determined interactions between the polymer chain segments, the interactions of the crosslinking metal ion with the polymer, and the deformation history of the network. Interpretations of mechanical and rheological measurements on polymer gels invariably begin with a conceptual model of,the microstructure of the gel network derived from polymer kinetic theory. In the present work, we use freeze-etch replication TEM to image the polymer network morphology of titanium crosslinked hydroxypropyl guars in an attempt to directly relate macroscopic phenomena with network structure.

Structures of c-di-GMP/cGAMP degrading phosphodiesterase VcEAL: identification of a novel conformational switch and its implication

2019 ◽  
Vol 476 (21) ◽  
pp. 3333-3353 ◽  
Author(s):  
Malti Yadav ◽  
Kamalendu Pal ◽  
Udayaditya Sen
Keyword(s):  
Active Site ◽  
Metal Binding ◽  
Metal Ion ◽  
Triosephosphate Isomerase ◽  
Catalytic Mechanism ◽  
Degradation Mechanism ◽  
Structural Basis ◽  
Conserved Residues ◽  
Phosphodiester Bond ◽  
Cyclic Dinucleotides

Cyclic dinucleotides (CDNs) have emerged as the central molecules that aid bacteria to adapt and thrive in changing environmental conditions. Therefore, tight regulation of intracellular CDN concentration by counteracting the action of dinucleotide cyclases and phosphodiesterases (PDEs) is critical. Here, we demonstrate that a putative stand-alone EAL domain PDE from Vibrio cholerae (VcEAL) is capable to degrade both the second messenger c-di-GMP and hybrid 3′3′-cyclic GMP–AMP (cGAMP). To unveil their degradation mechanism, we have determined high-resolution crystal structures of VcEAL with Ca2+, c-di-GMP-Ca2+, 5′-pGpG-Ca2+ and cGAMP-Ca2+, the latter provides the first structural basis of cGAMP hydrolysis. Structural studies reveal a typical triosephosphate isomerase barrel-fold with substrate c-di-GMP/cGAMP bound in an extended conformation. Highly conserved residues specifically bind the guanine base of c-di-GMP/cGAMP in the G2 site while the semi-conserved nature of residues at the G1 site could act as a specificity determinant. Two metal ions, co-ordinated with six stubbornly conserved residues and two non-bridging scissile phosphate oxygens of c-di-GMP/cGAMP, activate a water molecule for an in-line attack on the phosphodiester bond, supporting two-metal ion-based catalytic mechanism. PDE activity and biofilm assays of several prudently designed mutants collectively demonstrate that VcEAL active site is charge and size optimized. Intriguingly, in VcEAL-5′-pGpG-Ca2+ structure, β5–α5 loop adopts a novel conformation that along with conserved E131 creates a new metal-binding site. This novel conformation along with several subtle changes in the active site designate VcEAL-5′-pGpG-Ca2+ structure quite different from other 5′-pGpG bound structures reported earlier.

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