scholarly journals Metal bridge in S4 segment supports helix transition inShakerchannel

2019 ◽  
Author(s):  
Carlos A Z Bassetto ◽  
João Luis Carvalho-de-Souza ◽  
Francisco Bezanilla
Keyword(s):  
Secondary Structure ◽  
Metal Ion ◽  
Voltage Dependence ◽  
Helical Conformation ◽  
Activation Process ◽  
Structure Transition ◽  
Hydrophobic Residues ◽  
Voltage Gated ◽  
Α Helix ◽  
S4 Segment

ABSTRACTVoltage-gated ion channels play important roles in physiological processes, especially in excitable cells, where they shape the action potential. In S4-based voltage sensors voltage-gated channels, a common feature is shared: the transmembrane segment 4 (S4) contains positively charged residues intercalated by hydrophobic residues. Although several advances have been made in understating how S4 moves through a hydrophobic plug upon voltage changes, possible helix transition from α-to 310-helix in S4 during activation process is still unresolved. Here, we have mutated several hydrophobic residues from I360 to F370 in the S4 segment into histidine, ini, i+3andi, i+6ori, i+4andi, i+7pairs, to favor 310- or α-helical conformations, respectively. We have taken advantage that His can be coordinated by Zn+2to promote metal ion bridges and we have found that the histidine introduced at position 366 (L366H) can interact with the introduced histidine at position 370 (stabilizing that portion of the S4 segment in α-helical conformation). In presence of 20 μM of Zn+2, the activation currents of L366H:F370H channels were slowed down by a factor of 3.5, the voltage-dependence is shifted by 10 mV towards depolarized potentials with no change on the deactivation time constant. Our data supports that by stabilizing a region of the S4 segment in α-helical conformation a closed(resting or intermediate)state is stabilized rather than destabilizing the open (active)state. Taken together, our data indicates that the S4 undergoes α-helical conformation to a short-lived different secondary structure transiently before reaching theactivestate in the activation process.STATEMENT OF SIGNIFICANCEConformational transitions between α-helix and 310-helix in the S4 segment ofShakerpotassium channel during gating has been under debate. The present study shows the coordination by Zn2+of a pair of engineered histidine residues (L366H:F370H) in the intermediate region of S4 in Shaker, favoring α-helical conformation. In presence of 20μM of Zn+2the activation currents of L366H:F370H channels become slower, with 10 mV positive shift in the voltage-dependence and no effects on deactivation time constants suggesting a stabilization of a closed state rather than destabilization the open(active)state. Collectively, our data indicate that S4 undergoes secondary structure changes, including a short-lived secondary structure transition, when S4 moves from therestingto theactivestate during activation.

scholarly journals Metal-ion-binding properties of synthetic conantokin-G

1997 ◽  
Vol 328 (3) ◽  
pp. 777-783 ◽  
Author(s):  
Tamas BLANDL ◽  
Jaroslav ZAJICEK ◽  
Mary PROROK ◽  
J. Francis CASTELLINO
Keyword(s):  
Secondary Structure ◽  
Metal Ion ◽  
Hydration Number ◽  
Cation Binding ◽  
Helical Conformation ◽  
Cone Snail ◽  
Relaxation Rates ◽  
Ionic Radii ◽  
Single Class ◽  
Α Helix

The secondary structure of the synthetic 17-residue peptide, conantokin-G (con-G), a γ-carboxyglutamate-containing marine cone snail neuroactive protein, is altered from a random conformation to one containing a very high level (> 70%) of α-helix on binding of multivalent cations. The proportion of α-helix formed correlated well with the size of the cation and ranged from a low of approx. 7% with large cations, such as Ba2+, to more than 70% with smaller cations, such as Mn2+, Mg2+ and Zn2+. The valency of the multivalent cation was not as important, since tervalent lanthanides (Eu3+, Gd3+ and Tb3+) of ionic radius 106-109 pm induced similar levels (50-60%) of helix to those induced by Ca2+ and Cd2+ (ionic radii 109 and 114 pm respectively). Although the correlation was not as tight, smaller cations of the same valency allowed the helical transition to occur at lower concentrations than the larger cations. The spectroscopic and spectrometric properties of some of these cations permitted a more detailed analysis of the molecular nature of the cation-con-G binding. EPR-based titrations with Mn2+ provided a binding isotherm that was deconvoluted to a single class of 2-3 Mn2+ sites of average Kd 3.9 μM. This number of sites was similar to that for Ca2+ [Prorok, Warder, Blandl and Castellino (1996) Biochemistry 35, 16528-16534], but a much lower Kd was displayed with Mn2+. Determinations by 1H NMR of the longitudinal relaxation rates of the water protons in Mn2+/con-G solutions at different magnetic field strengths corresponding to the proton Langmuir frequencies of 24, 300 and 500 MHz permitted calculation of the hydration number of Mn2+ in the complex, which was found to be 1.0. This indicates that five of the six co-ordination sites of Mn2+ are occupied by peptide atoms, probably oxygens. Titrations of the changes in Tb3+ fluorescence as a result of its binding to con-G gave an EC50 of 58 μM, a value nearly identical with that obtained by titration of the change in helicity of the peptide as a function of Tb3+ concentration. This shows that the macroscopic binding of Tb3+ to con-G is directly responsible for the alteration in secondary structure of the peptide. Finally, Cd2+ was found to be an extremely suitable cation for an NMR-based investigation of the amino acid residues of apo-con-G that are perturbed by cation binding. In a limited example of the results of this study, it was discovered that originally equivalent CH2Δ protons of Arg13 became distinctly magnetically non-equivalent in the Cd2+-bound helical form of con-G. This indicates that Arg13 is situated in the helix in such a way that the mobility of its side chain is highly restricted. In conclusion, the data show that a variety of multivalent cations with measurable spectroscopic and spectrometric properties interact similarly with con-G and generate extensive α-helical conformation in this peptide.

From α-helix to β-sheet – a reversible metal ion induced peptide secondary structure switch

2005 ◽  
Vol 3 (14) ◽  
pp. 2500 ◽  
Author(s):  
Kevin Pagel ◽  
Toni Vagt ◽  
Tibor Kohajda ◽  
Beate Koksch
Keyword(s):  
Secondary Structure ◽  
Metal Ion ◽  
Α Helix ◽  
Peptide Secondary Structure ◽  
Β Sheet

scholarly journals Helical Structure of the Cooh Terminus of S3 and Its Contribution to the Gating Modifier Toxin Receptor in Voltage-Gated Ion Channels

2001 ◽  
Vol 117 (3) ◽  
pp. 205-218 ◽  
Author(s):  
Yingying Li-Smerin ◽  
Kenton J. Swartz
Keyword(s):  
Ion Channels ◽  
Secondary Structure ◽  
Terminal Part ◽  
Alanine Scanning Mutagenesis ◽  
K Channels ◽  
Voltage Gated ◽  
Gating Modifier ◽  
Α Helix ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

The voltage-sensing domains in voltage-gated K+ channels each contain four transmembrane (TM) segments, termed S1 to S4. Previous scanning mutagenesis studies suggest that S1 and S2 are amphipathic membrane spanning α-helices that interface directly with the lipid membrane. In contrast, the secondary structure of and/or the environments surrounding S3 and S4 are more complex. For S3, although the NH2-terminal part displays significant helical character in both tryptophan- and alanine-scanning mutagenesis studies, the structure of the COOH-terminal portion of this TM is less clear. The COOH terminus of S3 is particularly interesting because this is where gating modifier toxins like Hanatoxin interact with different voltage-gated ion channels. To further examine the secondary structure of the COOH terminus of S3, we lysine-scanned this region in the drk1 K+ channel and examined the mutation-induced changes in channel gating and Hanatoxin binding affinity, looking for periodicity characteristic of an α-helix. Both the mutation-induced perturbation in the toxin–channel interaction and in gating support the presence of an α-helix of at least 10 residues in length in the COOH terminus of S3. Together with previous scanning mutagenesis studies, these results suggest that, in voltage-gated K+ channels, the entire S3 segment is helical, but that it can be divided into two parts. The NH2-terminal part of S3 interfaces with both lipid and protein, whereas the COOH-terminal part interfaces with water (where Hanatoxin binds) and possibly protein. A conserved proline residue is located near the boundary between the two parts of S3, arguing for the presence of a kink in this region. Several lines of evidence suggest that these structural features of S3 probably exist in all voltage-gated ion channels.

Effect of Temperature and pH on the Secondary Structure and Denaturation Process of Jumbo Squid Hepatopancreas Cathepsin D.

2019 ◽  
Vol 26 (7) ◽  
pp. 532-541 ◽  
Author(s):  
Cadena-Cadena Francisco ◽  
Cárdenas-López José Luis ◽  
Ezquerra-Brauer Josafat Marina ◽  
Cinco-Moroyoqui Francisco Javier ◽  
López-Zavala Alonso Alexis ◽  
...  
Keyword(s):  
Circular Dichroism ◽  
Secondary Structure ◽  
Cathepsin D ◽  
Thermal Denaturation ◽  
Protein Denaturation ◽  
Marine Organisms ◽  
Effect Of Temperature ◽  
Jumbo Squid ◽  
Α Helix ◽  
Circular Dichroïsm

Background: Cathepsin D is a lysosomal enzyme that is found in all organisms acting in protein turnover, in humans it is present in some types of carcinomas, and it has a high activity in Parkinson's disease and a low activity in Alzheimer disease. In marine organisms, most of the research has been limited to corroborate the presence of this enzyme. It is known that cathepsin D of some marine organisms has a low thermostability and that it has the ability to have activity at very acidic pH. Cathepsin D of the Jumbo squid (Dosidicus gigas) hepatopancreas was purified and partially characterized. The secondary structure of these enzymes is highly conserved so the role of temperature and pH in the secondary structure and in protein denaturation is of great importance in the study of enzymes. The secondary structure of cathepsin D from jumbo squid hepatopancreas was determined by means of circular dichroism spectroscopy. Objective: In this article, our purpose was to determine the secondary structure of the enzyme and how it is affected by subjecting it to different temperature and pH conditions. Methods: Circular dichroism technique was used to measure the modifications of the secondary structure of cathepsin D when subjected to different treatments. The methodology consisted in dissecting the hepatopancreas of squid and freeze drying it. Then a crude extract was prepared by mixing 1: 1 hepatopancreas with assay buffer, the purification was in two steps; the first step consisted of using an ultrafiltration membrane with a molecular cut of 50 kDa, and the second step, a pepstatin agarose resin was used to purification the enzyme. Once the enzyme was purified, the purity was corroborated with SDS PAGE electrophoresis, isoelectric point and zymogram. Circular dichroism is carried out by placing the sample with a concentration of 0.125 mg / mL in a 3 mL quartz cell. The results were obtained in mdeg (millidegrees) and transformed to mean ellipticity per residue, using 111 g/mol molecular weight/residue as average. Secondary-structure estimation from the far-UV CD spectra was calculated using K2D Dichroweb software. Results: It was found that α helix decreases at temperatures above 50 °C and above pH 4. Heating the enzyme above 70°C maintains a low percentage of α helix and increases β sheet. Far-UV CD measurements of cathepsin D showed irreversible thermal denaturation. The process was strongly dependent on the heating rate, accompanied by a process of oligomerization of the protein that appears when the sample is heated, and maintained a certain time at this temperature. An amount typically between 3 and 4% α helix of their secondary structure remains unchanged. It is consistent with an unfolding process kinetically controlled due to the presence of an irreversible reaction. The secondary structure depends on pH, and a pH above 4 causes α helix structures to be modified. Conclusion: In conclusion, cathepsin D from jumbo squid hepatopancreas showed retaining up to 4% α helix at 80°C. The thermal denaturation of cathepsin D at pH 3.5 is under kinetic control and follows an irreversible model.

scholarly journals Secondary structure and biophysical activity of synthetic analogues of the pulmonary surfactant polypeptide SP-C

1995 ◽  
Vol 307 (2) ◽  
pp. 535-541 ◽  
Author(s):  
J Johansson ◽  
G Nilsson ◽  
R Strömberg ◽  
B Robertson ◽  
H Jörnvall ◽  
...  
Keyword(s):  
Secondary Structure ◽  
Pulmonary Surfactant ◽  
Transmembrane Helix ◽  
Helical Structure ◽  
Helical Conformation ◽  
Synthetic Analogues ◽  
Charged Amino Acids ◽  
Phospholipid Micelles ◽  
Helical Content ◽  
Biophysical Activity

Native pulmonary-surfactant-associated lipopolypeptide SP-C, its chemically depalmitoylated form and several synthetic analogues lacking the palmitoylcysteine residues were analysed for secondary structure in phospholipid micelles and for biophysical activity in 1,2-dipalmitoyl-sn-glycero-3- phosphocholine/phosphatidylglycerol/palmitic acid (68:22:9, by wt.). Compared with the native molecule, with the entire poly-valyl part in a known alpha-helical conformation, depalmitoylated SP-C was found to be still mainly alpha-helical, but with an approx. 20% decrease in the helical content. A synthetic hybrid polypeptide where the entire poly-valyl alpha-helical part of native SP-C had been replaced with the amino acid sequence of a transmembrane helix of bacteriorhodopsin is also predominantly alpha-helical. In contrast, synthetic SP-C analogues lacking only the palmitoyl groups, by replacement of the palmitoylcysteine residues with cysteine, phenylalanine or serine, or lacking the positively charged amino acids by replacement with alanine, are considerably less alpha-helical than both native and depalmitoylated SP-C. The data indicate that the SP-C palmitoyl groups are important for maintenance of the alpha-helical conformation in parts of the polypeptide, and that the poly-valyl alpha-helical conformation is not fully formed in synthetic SP-C polypeptides. Furthermore, the helical structure of both native and depalmitoylated SP-C in dodecylphosphocholine micelles is very resistant to thermal denaturation, exhibiting ordered structure at 90 degrees C. The alpha-helical content grossly parallels the peptide-induced acceleration of the spreading of phospholipids at an air/water interface and the increase of surface pressure. The data suggest that the alpha-helical conformation itself, rather than just the covalent structure, is of prime importance for the biological function of synthetic pulmonary-surfactant peptides.

Use of synchrotron-based FTIR microspectroscopy to determine protein secondary structures of raw and heat-treated brown and golden flaxseeds: A novel approach

2005 ◽  
Vol 85 (4) ◽  
pp. 437-448 ◽  
Author(s):  
P. Yu ◽  
J. J. McKinnon ◽  
H. W. Soita ◽  
C. R. Christensen ◽  
D. A. Christensen
Keyword(s):  
Secondary Structure ◽  
Matrix Protein ◽  
Protein Secondary Structure ◽  
Secondary Structures ◽  
Heat Processing ◽  
Lower Percentage ◽  
Protein Secondary Structures ◽  
Novel Approach ◽  
Α Helix ◽  
Β Sheet

The objectives of the study were to use synchrotron Fourier transform infrared microspectroscopy (S-FTIR) as a novel approach to: (1) reveal ultra-structural chemical features of protein secondary structures of flaxseed tissues affected by variety (golden and brown) and heat processing (raw and roasted), and (2) quantify protein secondary structures using Gaussian and Lorentzian methods of multi-component peak modeling. By using multi-component peak modeling at protein amide I region of 1700–1620 cm-1, the results showed that the golden flaxseed contained relatively higher percentage of α-helix (47.1 vs. 36.9%), lower percentage of β-sheet (37.2 vs. 46.3%) and higher (P < 0.05) ratio of α-helix to β-sheet than the brown flaxseed (1.3 vs. 0.8). The roasting reduced (P < 0.05) percentage of α-helix (from 47.1 to 36.1%), increased percentage of β-sheet (from 37.2 to 49.8%) and reduced α-helix to β-sheet ratio (1.3 to 0.7) of the golden flaxseed tissues. However, the roasting did not affect percentage and ratio of α-helix and β-sheet in the brown flaxseed tissue. No significant differences were found in quantification of protein secondary structures between Gaussian and Lorentzian methods. These results demonstrate the potential of highly spatially resolved S-FTIR to localize relatively pure protein in the tissue and reveal protein secondary structures at a cellular level. The results indicated relative differences in protein secondary structures between flaxseed varieties and differences in sensitivities of protein secondary structure to the heat processing. Further study is needed to understand the relationship between protein secondary structure and protein digestion and utilization of flaxseed and to investigate whether the changes in the relative amounts of protein secondary structures are primarily responsible for differences in protein availability. Key words: Synchrotron, FTIR microspectrosopy, flaxseeds, intrinsic structural matrix, protein secondary structures, protein nutritive value

scholarly journals Identification of a translocated gating charge in a voltage-dependent channel. Colicin E1 channels in planar phospholipid bilayer membranes.

1991 ◽  
Vol 98 (1) ◽  
pp. 77-93 ◽  
Author(s):  
C K Abrams ◽  
K S Jakes ◽  
A Finkelstein ◽  
S L Slatin
Keyword(s):  
Voltage Dependence ◽  
Ion Selectivity ◽  
Lipid Vesicles ◽  
Voltage Gating ◽  
Site Directed Mutagenesis ◽  
Phospholipid Bilayer ◽  
Voltage Gated ◽  
Colicin E1 ◽  
Gating Charge ◽  
Ion Conducting

The availability of primary sequences for ion-conducting channels permits the development of testable models for mechanisms of voltage gating. Previous work on planar phospholipid bilayers and lipid vesicles indicates that voltage gating of colicin E1 channels involves translocation of peptide segments of the molecule into and across the membrane. Here we identify histidine residue 440 as a gating charge associated with this translocation. Using site-directed mutagenesis to convert the positively charged His440 to a neutral cysteine, we find that the voltage dependence for turn-off of channels formed by this mutant at position 440 is less steep than that for wild-type channels; the magnitude of the change in voltage dependence is consistent with residue 440 moving from the trans to the cis side of the membrane in association with channel closure. The effect of trans pH changes on the ion selectivity of channels formed by the carboxymethylated derivative of the cysteine 440 mutant independently establishes that in the open channel state, residue 440 lies on the trans side of the membrane. On the basis of these results, we propose that the voltage-gated opening of colicin E1 channels is accompanied by the insertion into the bilayer of a helical hairpin loop extending from residue 420 to residue 459, and that voltage-gated closing is associated with the extrusion of this loop from the interior of the bilayer back to the cis side.

scholarly journals BeStSel: From Secondary Structure Analysis to Protein Fold Prediction by Circular Dichroism Spectroscopy

2020 ◽  
pp. 175-189
Author(s):  
András Micsonai ◽  
Éva Bulyáki ◽  
József Kardos
Keyword(s):  
Circular Dichroism ◽  
Secondary Structure ◽  
Classical Method ◽  
Cd Spectroscopy ◽  
Protein Fold ◽  
Cd Spectra ◽  
Secondary Structure Analysis ◽  
Β Sheets ◽  
Α Helix ◽  
Circular Dichroïsm

Abstract Far-UV circular dichroism (CD) spectroscopy is a classical method for the study of the secondary structure of polypeptides in solution. It has been the general view that the α-helix content can be estimated accurately from the CD spectra. However, the technique was less reliable to estimate the β-sheet contents as a consequence of the structural variety of the β-sheets, which is reflected in a large spectral diversity of the CD spectra of proteins containing this secondary structure component. By taking into account the parallel or antiparallel orientation and the twist of the β-sheets, the Beta Structure Selection (BeStSel) method provides an improved β-structure determination and its performance is more accurate for any of the secondary structure types compared to previous CD spectrum analysis algorithms. Moreover, BeStSel provides extra information on the orientation and twist of the β-sheets which is sufficient for the prediction of the protein fold. The advantage of CD spectroscopy is that it is a fast and inexpensive technique with easy data processing which can be used in a wide protein concentration range and under various buffer conditions. It is especially useful when the atomic resolution structure is not available, such as the case of protein aggregates, membrane proteins or natively disordered chains, for studying conformational transitions, testing the effect of the environmental conditions on the protein structure, for verifying the correct fold of recombinant proteins in every scientific fields working on proteins from basic protein science to biotechnology and pharmaceutical industry. Here, we provide a brief step-by-step guide to record the CD spectra of proteins and their analysis with the BeStSel method.

scholarly journals (De)stabilization of Alpha-Synuclein Fibrillary Aggregation by Charged and Uncharged Surfactants

2021 ◽  
Vol 22 (22) ◽  
pp. 12509
Author(s):  
Joana Angélica Loureiro ◽  
Stéphanie Andrade ◽  
Lies Goderis ◽  
Ruben Gomez-Gutierrez ◽  
Claudio Soto ◽  
...  
Keyword(s):  
Secondary Structure ◽  
Hydrophobic Interactions ◽  
Neurodegenerative Disorder ◽  
Sodium Dodecyl ◽  
Lewy Bodies ◽  
Alpha Synuclein ◽  
Cetyltrimethylammonium Chloride ◽  
Α Helix ◽  
Β Sheet

Parkinson’s disease (PD) is the second most common neurodegenerative disorder. An important hallmark of PD involves the pathological aggregation of proteins in structures known as Lewy bodies. The major component of these proteinaceous inclusions is alpha (α)-synuclein. In different conditions, α-synuclein can assume conformations rich in either α-helix or β-sheets. The mechanisms of α-synuclein misfolding, aggregation, and fibrillation remain unknown, but it is thought that β-sheet conformation of α-synuclein is responsible for its associated toxic mechanisms. To gain fundamental insights into the process of α-synuclein misfolding and aggregation, the secondary structure of this protein in the presence of charged and non-charged surfactant solutions was characterized. The selected surfactants were (anionic) sodium dodecyl sulphate (SDS), (cationic) cetyltrimethylammonium chloride (CTAC), and (uncharged) octyl β-D-glucopyranoside (OG). The effect of surfactants in α-synuclein misfolding was assessed by ultra-structural analyses, in vitro aggregation assays, and secondary structure analyses. The α-synuclein aggregation in the presence of negatively charged SDS suggests that SDS-monomer complexes stimulate the aggregation process. A reduction in the electrostatic repulsion between N- and C-terminal and in the hydrophobic interactions between the NAC (non-amyloid beta component) region and the C-terminal seems to be important to undergo aggregation. Fourier transform infrared spectroscopy (FTIR) measurements show that β-sheet structures comprise the assembly of the fibrils.

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