The effects of histone H4 tail acetylations on cation-induced chromatin folding and self-association

Understanding the molecular mechanisms behind regulation of chromatin folding through covalent modifications of the histone N-terminal tails is hampered by a lack of accessible chromatin containing precisely modified histones. We study the internal folding and intermolecular self-association of a chromatin system consisting of saturated 12-mer nucleosome arrays containing various combinations of completely acetylated lysines at positions 5, 8, 12 and 16 of histone H4, induced by the cations Na+, K+, Mg2+, Ca2+, cobalt-hexammine3+, spermidine3+ and spermine4+. Histones were prepared using a novel semi-synthetic approach with native chemical ligation. Acetylation of H4-K16, but not its glutamine mutation, drastically reduces cation-induced folding of the array. Neither acetylations nor mutations of all the sites K5, K8 and K12 can induce a similar degree of array unfolding. The ubiquitous K+, (as well as Rb+ and Cs+) showed an unfolding effect on unmodified arrays almost similar to that of H4-K16 acetylation. We propose that K+ (and Rb+/Cs+) binding to a site on the H2B histone (R96-L99) disrupts H4K16 ε-amino group binding to this specific site, thereby deranging H4 tail-mediated nucleosome–nucleosome stacking and that a similar mechanism operates in the case of H4-K16 acetylation. Inter-array self-association follows electrostatic behavior and is largely insensitive to the position or nature of the H4 tail charge modification

Study of the Interactions of D- and L- Polylysine Enantiomers with Pectate in Aqueous Solutions

The interaction between D- and L-enantiomers of polylysine and potassium pectate was studied by means of CD, microcalorimetry, and osmometry. Upon binding with pectate, only poly(L-lysine) undergoes a coil to α-helix transition, while poly(D-lysine) remains in the disordered state. This suggest that the energetics of the interaction is influenced by stereochemical constraints besides electrostatic forces. Experimental findings from microcalorimetry suggest that a contribution to the overall enthalpy of binding comes from the polysaccharidic moiety. Stoichiometry of the macromolecular complexes studied by osmometry gives a polylysine : pectate ratio of 3 : 1, in agreement with the respective degree of polymerization of the two polyelectrolyte

On the characterization of polygalacturonate salts in dilute solution

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A Conformational Study of the Diastereomeric Poly(lysine) - Pectate complexes.

The complex formation in aqueous solution between the polyelectrolytes poly(lysine) and pectate was studied focusing on the conformational changes of the polysaccharidic moiety. The findings suggest that the pectate adopts a superhelical conformation around the α helix of the poly(l-lysine). A threshold value of the degree of polymerization of the pectate chain enabling the transition of the peptide was determined by chromatographic and circular dichroism methods. Conformational analysis results are in agreement with the experimental findings and support the superhelical topology of the polyelectrolyte poly(l-lysine)−pectate complex

Electrostatic interactions in aqueous solutions of ionic polysaccharides

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The effect of neutral sugar distribution on the dilute solution conformation of sugar beet pectin

A partially degraded sugar beet pectin (C) was found to be heterogeneous in composition with neutral sugar-rich fractions of both high and low hydrodynamic radii. A neutral sugar-poor fraction was found at intermediate hydrodynamic radii. In this paper we demonstrate using both conformation zoning and the global analysis method that fractions of sugar beet pectin rich in neutral sugar side chains (RG-I regions) are less flexible than those rich in galacturonic acid (HG regions)