Chaperone activities of the 26S and 20S proteasome

The accumulation of misfolded or damaged proteins causes the failure of normal cell structure and functions necessary for growth and viability. To abort this adverse development, defective proteins must be rapidly repaired by molecular chaperones or destroyed by energy-dependent cytoplasmic proteases. A balance among these processes ultimately maintains cellular homeostasis. In eukaryotes, the 26S proteasome, a protease/chaperone complex, is a central component in the protein triage decision process. The 26S proteasome generally acts as a ubiquitination system, though it also selectively degrades structurally abnormal proteins in an ubiquitin-independent manner. In either case, all substrate proteins must undergo structural changes and stabilization necessary for their rapid degradation. It has, therefore, often been suggested that several chaperone functions are closely related to the stimulation of proteasomal degradation. This review summarizes recent discoveries pertaining to chaperone activities in the proteasomal degradation pathway, and to their regulation of protein breakdown mediated by the proteasome.     

Conformational changes of the S2YZ* intermediate of the S2 to S3 transition in photosystem II

The paper extends earlier studies on the S(2)Y(Z)* intermediate that is trapped by illumination in the temperature range 77 K to 190 K of untreated samples poised in the S(2)...Q(A) state. X-band EPR experiments on untreated and glycerol (50% v/v) treated samples at 10 K indicate that the intermediate consists of two components. A wide one with a splitting of ca 170 G, and a narrow one characterized by a splitting of ca 120 G (untreated), or 124 G (glycerol-treated samples). Lower temperatures of illumination in the above temperature range favor the wide component, which at 10 K decays faster than the narrow one. Re-illumination at 10 K after decay of the signal trapped at 77-190 K induces only the narrow component. Rapid scan experiments in the temperature range 77-190 K reveal high resolution spectra of the isolated tyz Z* radical and no evidence of alternative radicals. The two split signals are accordingly assigned to different conformations of the S(2)Y(Z)* intermediate A point-dipole simulation of the spectra yields "effective distances" between the spin densities of Y(Z)* and the Mn(4)Ca center of 5.7 ? for the wide and 6.4 ? for the narrow component. The results are discussed on the basis of a molecular model assuming two sequential proton transfers during oxidation of tyr Z. The wide component is assigned to a transient S(2)Y(Z)* conformation, that forms during the primary proton transfer.     

S1←S0 vibronic spectrum and structure of fluoral in the S1 state

The vibronic absorption spectrum of fluoral vapor was studied in the region of the S₁←S₀ electronic transition (313–360 nm). The origin O₀ ⁰⁺) of the transition (29419 cm⁻¹) and a number of fundamental frequencies in the S₀ and S₁ states were determined. The character of intensity distribution in the spectral bands indicates that the electronic excitation leads to significant change of the CF₃ group orientation relative to the molecular frame. Moreover, it was found that the carbonyl fragment of the molecule in the S₁ state has pyramidal structure (in contrast, the carbonyl fragment of the fluoral molecule in the S₀ state is planar). The experimental torsion and inversion energy levels were used for the calculation of internal rotation and inversion potential functions of fluoral molecule in the S₁ state. The potential barriers to internal rotation and inversion were found to be 1270 cm⁻¹ (15.2 kJ mol⁻¹) and 550 cm⁻¹ (6.6 kJ mol⁻¹), respectively. The conformational changes caused by S₁←S₀ electronic excitation in the fluoral molecule are similar to those observed in acetaldehyde and biacetyl molecules and differ from the conformational behavior of hexafluorobiacetyl molecule. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 294–299, February, 1998.     

Section EuNdGa3S7-EuGa4S7 of the ternary system Nd2S3-Ga2S3-EuS

The section EuNdGa₃S₇-EuGa₄S₇ of the ternary system Nd₂S₃-Ga₂S₃-EuS was studied by physicochemical analysis methods (differential thermal, X-ray powder diffraction, and microstructural analyses and microhardness and density measurements). The data obtained were used to construct the state diagram of the section EuNdGa₃S₇-EuGa₄S₇. The section was found to be a quasi-binary section of the ternary system and is of the eutectic type. The coordinates of the eutectic are 64 mol % EuGa₄S₇ and T _melt = 1170 K. A region of solid solutions based on both components was found.     

Vibronic spectral behavior of molecules. XIII. Theoretical contribution to the vibronic coupling and the dushinsky effect on the S1 ← S0 absorption and the S1 → S0, S2 → S1, and S2 → S0 fluorescences of azulene

Based on the completely optimized S₀, S₁, and S₂ molecular geometries of azulene, the vibronic structure of the S₁ ← S₀ absorption as well as of the S₁ → S₀, S₂ → S₁, and S₂ → S₀ fluorescences is investigated theoretically within the adiabatic approximation. By means of theory-experiment comparisons, the influence of non-Condon terms and of the Dushinsky effect on the vibronic structure of azulene spectral behavior is discussed. Typical for the S₁ ← S₀ absorption and the S₁ → S₀ fluorescence are vibronic transition moment contributions of Condon type, whereas the interpretation of azulene S₂ → S₁ and S₂ → S₀ fluorescences is successful only within the scope of the Herzberg–Teller approach by taking into account vibronic coupling terms and, additionally, the Dushinsky effect in the latter case. An analysis of the relevant vibrational modes is given.     

Two-photon laser spectroscopy of the muonium 1S–2S transition

The 1² S _1/2(F=1)?2² S _1/2(F=1) energy interval in muonium has been investigated by Doppler-free two-photon laser spectroscopy. The transition was observed by uniquely identifying and counting the muons released after the photoionization of the 2S state by the same laser field. The measured transition frequency of 2455 528016(58)(43) MHz is in good agreement with QED calculations. The experiment can be interpreted as a test of the Lamb shift contributions at the 1% level. The method is also well suited for a precise determination of the mass of the positive muon in a muoniumhydrogen isotope shift measurement.     

Stability analysis of the two rotational isomers of meta-fluorobenzaldehyde in the S0, S1, and S2 electronic states

For a determination of the stabilization energy between the two rotational isomers of m-fluorobenzaldehyde, the S(1,2)<--S0 absorption spectra were observed in fluid n-hexane solutions at 293 and 198 K. After employing a simulation method for the spectra, we succeeded in determining the stabilization energies in the ground and the relevant excited state at the same time. The energy was estimated to be 1.7 +/- 0.5 kJ mol(-1) for S0 and also for S1 while it was 2.9 +/- 0.5 kJ mol(-1) for S2. Ab initio calculations at MP2/6-311G** computational level predicted that the O-cis form in the S0 state is more stable by 1.9 +/- 0.5 kJ mol(-1) than the counterpart rotamer, O-trans form. In summary, a schematic energy level diagram of the two rotational isomers will be illustrated for the S0, S1, and S2 states in the fluid system.     

S2 fluorescence and ultrafast relaxation dynamics of the S2 and S1 states of a ketocyanine dye

Dynamics of the excited singlet (both the S2 and S1) states of a ketocyanine dye, namely, 2,5-bis[(2,3-dihydroindolyl)-propylene]-cyclopentanone (KCD), have been investigated in different kinds of media using steady-state absorption and emission as well as femtosecond transient absorption spectroscopic techniques. Steady-state fluorescence measurements, following photoexcitation of KCD to its second excited singlet state, reveal dual fluorescence (emission from both the S2 and S1 states) behavior. Although the intensity of the S2 --> S0 fluorescence is weaker than that of the S1 --> S0 fluorescence in solutions at room temperature (298 K), the former becomes as much as or more intense than the latter in rigid matrixes at 77 K. The lifetime of the S2 state is short and varies between 0.2 and 0.6 ps in different solvents. After its creation, the S2 state undergoes two simultaneous processes, namely, S2 --> S0 fluorescence and S2 --> S1 internal conversion. Time-resolved measurements reveal the presence of an ultrafast component in the decay dynamics of the S1 state. A good correlation between the lifetime of this component and the longitudinal relaxation times (tauL) of the solvents suggests that this component arises due to solvation in polar solvents. More significant evolution of the spectroscopic properties of the S1 state in alcoholic solvents in the ultrafast time domain has been explained by the occurrence of the repositioning of the hydrogen bonds around the carbonyl group in the excited state of KCD. In 2,2,2-trifluoroethanol, a strongly hydrogen bond donating solvent, it has even been possible to establish the existence of two distinct forms of the S1 state, namely, the non-hydrogen-bonded (or free) molecule and the hydrogen-bonded complex.     

Effect of Sπ on the Polymerization of Liquid Sulfur and the Nature of Sπ

The Tobolsky-Eisenberg theory serves to explain the equilibrium polymerization of sulfur in terms of the dependence of S₈ (ring) concentration on temperature and the dependence of number-average degree of polymerization on temperature. The predictions of the theory are completely in accord with experiment. In this paper it is shown that it is possible to take the presence of another component in the melt, Sπ, into account, using a slightly modified version of the Tobolsky-Eisenberg theory. When this is done it is found that the earlier conclusions remain valid. The molecular complexity and structure of Sπ is also discussed.     

Coordination properties of the multifunctional S,N,S zwitterionic ligand EtNHC(S)Ph2PNPPh2C(S)NEt

The reaction of trialkylphoshanes and amino-phosphanes with isothiocyanates yields adducts containing the zwitterionic thioamidyl-phosphonium P⁺C(S)N^? functional group. Ligands containing this group were not previously studied, probably due to their instability towards dissociation, in the presence of metal species able to coordinate the P atom. The ligand EtNHC(S)Ph₂PNPPh₂C(S)NEt (HEtSNS) was obtained by reaction of Ph₂PNHPPh₂ with ethylisothiocyanate and proved to be very versatile: it can be protonated giving cation H₂EtSNS⁺ and deprotonated forming the dianion–cation EtSNS^?. HEtSNS and its derivatives behave as ligands showing five possible coordination fashions, S,N,S tridentate and S,S-bidentate (with a bite-angle varying from 180° to 90°), S-monodentate, S,S bridging and N,N,N interaction. Here we describe the coordination chemistry of HEtSNS, in particular towards Rh, Cu, Ag and Au, and some properties of its complexes which are still the only examples containing the P⁺C(S)N^? zwitterionic group.     

Energies of the lowest singlet S and triplet S states of helium by the local energy method

The least squares local energy method is applied to the helium atom in greater detail in a formulation which can easily be extended to more complicated atoms. The energies of the 1 ¹ S and 2³ S states are calculated to be – 2.9025 H and – 2.1753 H respectively. These values are in excellent agreement with the non-relativistic values of – 2.9037 H and – 2.1752 H calculated by Pekeris.

---

Zusammenfassung Die Methode, die Varianz der lokalen Energie zu minimisieren, wird in einer leicht auf kompliziertere Atome zu erweiternden Form ausführlicher auf das Heliumatom angewandt. Die Energien des 1 ¹ S – und des 2 ³ S–Zustandes werden zu – 2,9025 bzw. – 2,1753 at. E. berechnet. Diese Werte stimmen ausgezeichnet mit den von Pekeris berechneten nichtrelativistischen Werten von – 2,9037 bzw. – 2,1752 at. E. überein.

---

Résumé Le calcul de l'énergie locale par la méthode des moindres carrés est appliqué plus en détail à l'atome d'hélium, dans une forme qui s'étend aisément à des atomes plus compliqués. Les énergies des états 1 ¹ S et 2 ³ S se calculent à – 2,9025 et – 2,1753 u. a., respectivement. Ces valeurs sont en excellent accord avec les valeurs de – 2,9037 et – 2,1752 u. a. (sans relativité) calculées par Pekeris.

     

Interaction in the Yb2S3-In2S3 system

A T-x diagram is designed for the Yb₂S₃-In₂S₃ system using physicochemical methods. A complex chemical reaction occurs in the system to yield ternary compounds Yb₃InS₆ (S₁), YbInS₃ (S₂), Yb₃In₅S₁₂ (S₃), and YbIn₃S₆ (S₄). In₂S₃-based limited solid solutions are found. Phases S₁, S₃, and S₄ are formed by peritectic reactions at 1260, 1200, and 1100 K, respectively. Compound S₂ melts congruently at 1390 K. Compound S₃ crystallizes in monoclinic system (a = 10.90 Å, b = 21.01 Å, c = 3.846 Å, β = 96.2°). Compounds S₁ and S₄ crystallize in orthorhombic system (for S₁, a = 16.76 Å, b = 13.70 Å, c = 3.88 Å; for S₄, a = 3.86 Å, b = 11.64 Å, c = 20.98 Å, d _exp = 4.62 g/cm³). Compound S₂ crystallizes in cubic system (a = 10.68 Å).     

Moderately high resolution fluorecence spectrum of the S1 → S0 transition of azulene

We report an Ar/Kr ion laser induced spectrally resolved S₁ → S₀ emission from an azulene in a host naphthalene crystal observed at the helium λ-point and at 77 K. Less well resolved S₁ → S₀ emission from crystalline azulene dispersed in a KBr pellet at 300 K is also reported. For the 6471 Å excitation the emission from the azulene in naphthalene system is analyzed in terms of three components: a resonance enhanced Raman emission originating from a nonstationary laser photon energy state 800 cm^?1 above the S₁ origin, a partially relaxed fluorecence originating from the 665 cm^?1 vibrational level of S₁ and a totally relaxed fluorecence from the S₁ origin (14651 cm^?1). The interpretation of the spectral lines is based on totally symetric vibrational modes (406, 679, 825,902, 1203, 1269, 1401, and 1586 cm^?1) the most prominent of which is the progression forming 825 cm^?1 mode. On the basis of both energies and intensities, correlations are made between ground and excited state vibrations and are compared with earlier results. Based on our results, a discussion is given on a plausible relaxation scheme for our system including the influence of Franck—Condon factors on the observability of unrelaxed emission.     

Mechanisms for proton release during water oxidation in the S2 to S3 and S3 to S4 transitions in photosystem II

The new high-resolution X-ray structure of photosystem II has allowed more detailed studies than before of water oxidation at the oxygen evolving complex (OEC). In the present study the two final S-transitions of water oxidation are studied. The electron coupled proton transfers are followed from the center of the OEC to Asp61, which is considered as the start of the transfer chain through the protein to the lumenal side. It is found that the proton transfers occur in multiple steps. Structures of intermediates and energy diagrams are derived and compared to experimental observations. Since the new experimental structure of the OEC is very similar to the one suggested earlier by density functional calculations, the O-O bond formation step remains essentially the same as the one suggested five years ago. An interesting new result is that the barrier for proton transfer within the OEC actually competes with the O-O bond formation step of being rate-limiting.     

具有S…S、S…Cl作用的一维链状有机锡化合物氯代二苄基锡哌啶荒酸酯的合成、表征及晶体结构

The chlorodibenzyltin dithiopiperidylcarbamate was synthesized by the reaction of dibenzyltin dichloride withdithiopiperidylcarbamate and was characterized by elemental analysis, IR and 1H NMR. The crystal structure wasdetermined by X-ray single crystal diffraction. The crystallographic data are as follows: monoclinic, space groupP21, a=0.63464(13) nm, b=1.9110(4) nm, c=0.87367(17) nm, β3=97.67(3)°, Z=2, V=1.0501(4)nm3, Dc=1.571g @ cm-3, μ= 1.546mm-1, F(000) =500, R=0,0209, wR=0.0381 [I≥ 2σ(Ⅰ)]. The str-uctures consist of discrete molecules containing five-coordinate tin atoms in a seriously distorted trigonal bipyramidalconfiguration. The molecules are packed in the unit cell in one-dimensional chain complex through a weak inter-action between the chlorine atom, the sulfur atom and one of the other sulfurs of an adjacent molecule.     

The 11S proteasome activator: Isolation from mouse brain and the influence on peptide substrate hydrolysis of the 20S and 26S proteasomes

Purification of the 11S proteasome regulator from mouse brain was optimized; the subunit composition of the isolated protein was determined by Western blot. The dependency of 20S proteasome peptidase activity on the molar concentration of the 11S regulator was examined. The Michaelis constants of hydrolysis of the specific fluorescent substrates Suc–Leu–Leu–Val–Tyr–AMC, Ac–Arg–Leu–Arg–AMC, and Z–Leu–Leu–Glu–AMC by the 20S proteasome from BALB/c mouse brain and the 20S–11S complex were determined. It was shown that the 11S particle has almost no influence on binding of specific fluorescent substrates to the 20S proteasome, but strongly accelerates hydrolysis of all three substrates, while not affecting the rate of peptide substrate hydrolysis by the 26S proteasome.