Biomedical subjects

X W Guo

Publications and source records attributed to X W Guo.

5 recordsLinked to original sources

PubMed1992

Binding of a synthetic targeting peptide to a mitochondrial channel protein.

Membrane crystals of the mitochondrial outer membrane channel VDAC (porin) from Neurospora crassa were incubated with a 20-amino-acid synthetic peptide corresponding to the N-terminal targeting region of subunit IV of cytochrome oxidase. The peptide caused disordering and contraction of the crystal lattice of the membrane arrays. Also, new stain-excluding features were observed on the peptide-treated arrays which most likely correspond to sites at which the peptide accumulates. The stain exclusion zones associated with binding of the targeting peptide (and with binding of apocytochrome c in an earlier study) have been localized on a two-dimensional density map of frozen-hydrated, crystalline VDAC previously obtained by cryo-electron microscopy. The results indicate that both the peptide and cytochrome c bind to protein "arms" which extend laterally between the channel lumens. The finding that imported polypeptides bind to a specific region of the VDAC protein implicates this channel in the process by which precursor proteins are recognized at and translocated across the mitochondrial outer membrane.

Amino Acid Sequence↗

PubMed1992

Classification of projection images of crystalline arrays of the mitochondrial, voltage-dependent anion-selective channel embedded in aurothioglucose.

Low-dose electron microscopic images have been recorded from membrane crystals of the mitochondrial, voltage-dependent anion-selective channel, embedded in aurothioglucose. There is considerable variation in the high-resolution detail present in correlation averages computed from these images. Correspondence analysis reveals three classes of "control" averages, with main components of variation involving projected size of the pores and density modulations around the pores and in the corners of the unit cells away from the pores. Pretreatments that affect the functional state of the channel also affect the array averages. In particular, there appears to be a general correlation between the expected effector-induced state (i.e., open and closed) and the projected diameter of the channel lumens in the crystalline arrays.

Aurothioglucose↗

PubMed1990

Interaction between the VDAC channel and a polyanionic effector. An electron microscopic study.

The conductance of the voltage-dependent mitochondrial outer membrane channel is modulated by a synthetic anionic polymer. When added to suspensions of membrane crystals of the channel, the polyanion caused disordering of the usual parallelogram array and increased occurrence of a contracted form of the array. Correlation averages obtained from electron microscopic images of the channel crystals indicated a narrowing of the projected channel lumen in the presence of the polyanion and the appearance of new, narrow zones of stain exclusion on the outside of the channel. These effects are interpreted in terms of possible conformational changes induced in the channel by binding of the polyanion.

Electric Conductivity↗

PubMed1989

Chromatin aggregation depends on the anion species of the salts.

The effects of anions on chromatin aggregation may be classified into three categories. First, monovalent anions, glutamate, acetate, chloride, and thiocyante, follow the lyotropic series in their effects on both H1 histone displacement and chromatin aggregation. Second, alkyl carboxylates and dicarboxylates differ in their ability to induce chromatin aggregation depending on charge density, suggesting possible interference by bulky alkyl chains with neutralization (screening) of closely spaced positive protein charges. Third, the multivalent anions, citrate3- and SO4(2-), bind tightly to histone and disrupt nucleosomes and thus interfere with chromatin aggregation. Substantial differences in chromatin aggregation were observed with different species of anions. At salt concentrations of 0-500 mN and pH 7.0, as much as 70% of the chromatin could be induced to aggregate by monosodium glutamate and sodium acetate, whereas only 10% or less was precipitated by NaSCN, Na2SO4, and Na3citrate. The physiological anion composition of the nucleus is not known; however, the anion effects discussed in the present work suggest a potential for regulation of chromatin condensation in higher eukaryotes.

Acetates↗

PubMed1989

Chromatin aggregation changes substantially as pH varies within the physiological range.

In vitro at least, changes of pH within the physiological range are important in regulating chromatin aggregation. The extent of aggregation was shown to depend substantially on pH as well as on salt. In the absence of salt and in all of the salt conditions tested as the pH was increased, less and less chromatin was aggregated. The aggregation of half the chromatin in the presence of 0 mM NaCl, 150 mM NaCl, 150 mM NaCl and 1 mM MgCl2, and 2 mM MgCl2 was observed at pH 5.4, 6.0, 7.0, and 8.3, respectively. In 150 mM NaCl, 1 mM MgCl2, chromatin aggregation decreased from 86 to 63% as the pH was changed from 5.9 to 6.8, which is the same pH change reported to occur between interphase and mitosis. H1 dissociation from chromatin was also found to be pH dependent.

Chromatin↗