Point Mutations of Nicotinic Receptor α1 Subunit Reveal New Molecular Features of G153S Slow-Channel Myasthenia

Slow-channel congenital myasthenic syndromes (SCCMSs) are rare genetic diseases caused by mutations in muscle nicotinic acetylcholine receptor (nAChR) subunits. Most of the known SCCMS-associated mutations localize at the transmembrane region near the ion pore. Only two SCCMS point mutations are at the extracellular domains near the acetylcholine binding site, α1(G153S) being one of them. In this work, a combination of molecular dynamics, targeted mutagenesis, fluorescent Ca²⁺ imaging and patch-clamp electrophysiology has been applied to G153S mutant muscle nAChR to investigate the role of hydrogen bonds formed by Ser 153 with C-loop residues near the acetylcholine-binding site. Introduction of L199T mutation to the C-loop in the vicinity of Ser 153 changed hydrogen bonds distribution, decreased acetylcholine potency (EC₅₀ 2607 vs. 146 nM) of the double mutant and decay kinetics of acetylcholine-evoked cytoplasmic Ca²⁺ rise (τ 14.2 ± 0.3 vs. 34.0 ± 0.4 s). These results shed light on molecular mechanisms of nAChR activation-desensitization and on the involvement of such mechanisms in channelopathy genesis.     

The exterior magnetic field for the multilayer ellipsoidal model of the brain

The magnetic induction field in the exterior of an ellipsoidallyinhomogeneous, four-conducting-layer model of the human headis obtained analytically up to its quadrupole approximation.The interior ellipsoidal core represents the homogeneous brainwhile each one of the shells represents the cerebrospinal fluid,the skull and the scalp, all characterized by different conductivities.The inhomogeneities of these four domains, together with theanisotropy imposed by the use of the ellipsoidal geometry, providethe most realistic physical and geometrical model of the brainfor which an analytic solution of the biomagnetic forward problemis possible. It is shown that in contrast to the spherical model,where shells of different conductivity are magnetically invisible,the magnetic induction field in ellipsoidal geometry is stronglydependent on the conductivity supports. The fact that sphericalshells of different conductivity are invisible has enhancedthe common belief that the biomagnetic forward solution doesnot depend on the conductivity profiles. As we demonstrate inthe present work, this is not true. Hence, the proposed multilayeredellipsoidal model provides a qualitative improvement of therealistic interpretation of magnetoencephalography (MEG) measurements.We show that the presence of the shells of different conductivitycan be incorporated in the form of the dipole vector for thehomogeneous model. Numerical investigations show that the effectsof shell inhomogeneities are almost as sound as the level ofMEG measurements themselves. The degenerate cases, where eitherthe differences of the conductivities within the shells disappear,or the ellipsoidal geometry is reduced to the spherical one,are also considered.     

Synthesis and photochemical properties of the indoline series fulgides

Using the Stobbe condensation fulgides that undergo E, Z-isomerization on exposure to UV radiation are obtained from diethyl [2-(1,3,3-trimethyindoline-2-ilidene)ethylidene]succinate, and benzaldehyde and its derivatives; and from 1,2-dimethyl-3-formylindole and -formyl-1,3,3-trimethyl-2-methyleneindoline. The structure and photochemical changes of the fulgides were investigated by means of PMR.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 55–60, January, 1992.     

Photoacclimation in spathiphyllum

We studied photoacclimation in Spathiphyllum grown at an irradiance of 40 or 420 micromol/m2 s (LL or HL, respectively). All parameters studied responded to acclimation. Leaves at LL, in contrast to HL, were thinner and oriented perpendicular to the incident light, had more chlorophyll per g f w, fewer stomata on the upper leaf surface and a reduced layer of mesophyll cells. Their chloroplasts at HL had wider grana with less thylakoids per granum, and better organized photosystems than at LL. PSI and PSII activities per mg chlorophyll ( Vmax ), and PSI and PSII content (total activity per g f w), were lower at LL than at HL and so was the light requirement for saturation of the PSI or PSII partial photoreactions, suggesting that fewer photosystems with larger antenna size prevail at LL, but many more with smaller antenna size at HL. Analysis of chlorophyll distribution among the thylakoid pigment-protein complexes showed less antenna chlorophyll serving PSII (CPa+LHCP1+LHCP3) than that serving PSI (CPIa+CPI+LHCP2) at LL as compared to HL, and thus a lower PSII/PSI ratio at LL, in agreement with the general finding that LL plants, with larger PSII antenna size, have lower PSII/PSI ratio. The increase in PSI antenna size at LL was correlated with the increase in the distribution of chlorophyll in pigment-protein complexes serving PSI, and a very large chlorophyll/protein molar ratio in the isolated CPI complex. On the other hand, the PSII antenna chlorophyll (CPa+LHCP1+LHCP3) on a g f w basis, and the chlorophyll a/b ratio remained more or less constant at LL or HL. This may reflect our finding that Spathiphyllum contains mainly the 27 kDa inner LHCII antenna protein, the size of which remains unaffected by photoacclimation. The increase in the distribution of chlorophyll in pigment-protein complexes serving PSII at HL, therefore, reflects the higher population of PSII at HL. Very high PSI activity was found at HL, which we attribute to the highly organized small in size PSI.     

Comparison of reactivities of 1- and 4-oxotetrahydrocarbazoles in reactions with nucleophilic and electrophilic reagents

The half-wave potentials of polarographic reduction of the carbonyl group in unsubstituted and N-methyl- and N-phenylsulfonyl-substituted 1- and 4-oxotetrahydrocarbazoles and their reactivities in reactions with nucleophilic (NaBH₄, malonodinitrile, and cyanoacetamide) and electrophilic (DMF dimethyl acetal) reagents were compared. 4-Oxotetrahydrocarbazoles are much less reactive than 1-oxotetrahydrocarbazoles. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1832–1836, August, 2005.     

Chromium(V) peptide complexes: synthesis and spectroscopic characterization

A series of stable Cr(V) model complexes that mimic the binding of Cr(V) to peptide backbones at the C-terminus of proteins have been prepared for N,N-dimethylurea derivatives of the tripeptides Aib3-DMF, AibLAlaAib-DMF, and AibDAlaAib-DMF (Aib = 2-amino-2-methylpropanoic acid, DMF = N,N-dimethylformamide). The Cr(ll) precursor complexes were synthesized by the initial deprotonation of the amide and acid groups of the peptide ligands in DMF with potassium tert-butoxide in the presence of CrCl2. The Cr(II) intermediates thus formed were then immediately oxidized to Cr(V) using tert-butyl hydroperoxide. Spectroscopic and mass-spectrometric analyses of the Cr(V) complexes showed that a new metal-directed organic transformation of the ligand had occurred. This involved a DMF solvent molecule becoming covalently bound to the amine group of the peptide ligand, yielding a urea group, and a third coordinated deprotonated urea nitrogen donor. A metal-directed oxidative coupling has been proposed as a possible mechanism for the organic transformation. The Cr(V/IV) reduction potential was determined for the three Cr(V) complexes using cyclic voltammetry, and in all cases it was quasi-reversible. These are the first isolated and fully characterized Cr(V) complexes with non-sulfur-containing peptide ligands.     

A new steroid glycoside from the starfishPatiria pectinifera

From the glycoside fraction of the starfishPatiria pectinifera, after its desulfation, an artefactural glycoside has been obtained: 29(-L-arabinofuranosyloxy)-5-stigmastane-3,6,8,15,16-pentaol (I). The structure of (I) was shown by¹H and¹³C NMR spectra and mass spectra and by acetylation and high-temperature hydrogenation.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Scientific Center, Academy of Sciences of the USSR, Vladivostok. Institute of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 356–361, May–June, 1985.