III. Foldamer Research 3910 A. Overview 3910 B. Motivation 3910 C. Methods 3910 D. General Scope 3912 IV. Peptidomimetic Foldamers 3912 A. The R-Peptide Family 3913 1. Peptoids 3913 2. N,N-Linked Oligoureas 3914 3. Oligopyrrolinones 3915 4. Oxazolidin-2-ones 3916 5. Azatides and Azapeptides 3916 B. The â-Peptide Family 3917 1. â-Peptide Foldamers 3917 2. R-Aminoxy Acids 3937 3. Sulfur-Containing â-Peptide Analogues 3937 4. Hydrazino Peptides 3938 C. The γ-Peptide Family 3938 1. γ-Peptide Foldamers 3938 2. Other Members of the γ-Peptide Family 3941 D. The δ-Peptide Family 3941 1. Alkene-Based δ-Amino Acids 3941 2. Carbopeptoids 3941 V. Single-Stranded Abiotic Foldamers 3944 A. Overview 3944 B. Backbones Utilizing Bipyridine Segments 3944 1. Pyridine−Pyrimidines 3944 2. Pyridine−Pyrimidines with Hydrazal Linkers 3945

A field guide to foldamers.

Calcium in Plants

Cloning and sequence analysis of cDNA for the Electrophorus electricus electroplax sodium channel indicate that this protein, consisting of 1,820 amino acid residues, exhibits four repeated homology units, which are presumably oriented in a pseudosymmetric fashion across the membrane. Each homology unit contains a unique segment with clustered positively charged residues, which may be involved in the gating structure, possibly in conjunction with negatively charged residues clustered elsewhere.

Primary structure of Electrophorus electricus sodium channel deduced from cDNA sequence.

### Calcium Signals: A Central Paradigm in Stimulus–Response Coupling

Cells must respond to an array of environmental and developmental cues. The signaling networks that have evolved to generate appropriate cellular responses are varied and are normally composed of elements that include a

Calcium at the Crossroads of Signaling

http://www.bio21.bas.bg/ibf/PC_review.pdf

Phases and phase transitions of the phosphatidylcholines

Pore formation of alamethicin has been studied by the analysis of steadystate fluctuations of single-pore conductances. An aggregation model is proposed where transitions to the next higher or lower pore state occur by uptake or release of one monomer. It is assumed that alamethicin forms an elongated loop in the bilayer. The main voltage-dependent step is the insertion of this monomer into the membrane after complexation with a cation. This mechanism is equivalent to dipole orientation in an electric field. Pore formation is restricted by the energy required to enlarge the channel in the membrane.

Statistical analysis of alamethicin channels in black lipid membranes.

The lipid bilayer technique was adapted to the functional reconstitution of ion channels from the endoplasmic reticulum of a higher plant. This was obtained at high purity from touch-sensitive tendrils of Bryonia dioica. In this preparation, a calcium-selective strongly rectifying channel is prevailing whose single-channel properties have been characterized. The single-channel conductance is 29 pS in 50 mM CaCl2. The Ca2+: K+ selectivity was determined to be approximately 6.6. The channel is voltage-gated and, more importantly, the gating voltage is strongly shifted towards more negative voltages when a transmembrane Ca2+ gradient is applied. Thus, at physiological voltages across the endoplasmic reticulum membrane, the channel's open probability will be governed largely by the chemical potential gradient of Ca2+, generated by the Ca(2+)-ATPase in that same membrane. The calcium release channel described here is effectively blocked by Gd3+ which also completely suppresses a tendril's reaction to touch, suggesting that this channel could be a key element of calcium signaling in higher plant mechanotransduction. Its molecular characteristics and inhibitor data show it to be the first known member of a hitherto unrecognized class of calcium channels.

/pdf/gadolinium-sensitive-voltage-dependent-calcium-release-1447475adv.pdf

Gadolinium-sensitive, voltage-dependent calcium release channels in the endoplasmic reticulum of a higher plant mechanoreceptor organ.

The voltage-dependency of alamethicin pore formation is explained by a flip-flop gating mechanism of single alamethicin molecules. The energetically preferred aggregate structure is changed from antiparallel to parallel molecule orientation by membrane voltage application. The electrical field is sensed by the permanent dipole of the α-helical molecule part which spans the hydrophobic membrane core. Ion conducting pore and pore states result from electrostatic repulsion of a varying number of parallel dipoles which arrange circularly. This model is consistent with published data and with two additional experimental facts, that pore state distributions are ionic strength dependent and pore state conductances depend on ionic current direction.

Alamethicin pore formation: Voltage-dependent flip-flop of α -helix dipoles

Melittin and a chemically modified trichotoxin form alamethicin-type multi-state pores

The electrical properties of an alamethicin multi-pore system have been studied by voltage-jump current-relaxation experiments (this paper) and by autocorrelation and spectral analysis (following paper). With these methods a slow time constant and a fast time constant were observed which differ by about one to three orders of magnitude depending on the experimental conditions. Steady-state current and time constants were analyzed as functions of voltage, alamethicin concentration and temperature. Within experimental error the data obtained with these different methods are in good agreement. The experimentally measured relation between the voltage and alamethicin concentration dependence of the slow relaxation time fits into a model of an alamethicin pore which adopts consecutive pore states and which decays only from the lowest state. It indicates that the uptake of one alamethicin molecule by the existing pore and, in formal equivalence, the transfer of about one positive elementary charge across the membrane are associated with the transition from a given pore conductance state to the next higher state. From the voltage and alamethicin concentration dependence of the pore formation rate evidence shows that a hexameric preaggregate exists at the membrane interface out of which two to three molecules are simultaneously inserted into the membrane to form the pore nucleus. The effects of different voltage pretreatment on the experimentally determined parameters have been investigated and are discussed in detail.

Günther Boheim

Papers

Statistical analysis of alamethicin channels in black lipid membranes.

Gadolinium-sensitive, voltage-dependent calcium release channels in the endoplasmic reticulum of a higher plant mechanoreceptor organ.

Alamethicin pore formation: Voltage-dependent flip-flop of α -helix dipoles

Melittin and a chemically modified trichotoxin form alamethicin-type multi-state pores

Analysis of the multi-pore system of alamethicin in a lipid membrane