Biomedical subjects

Y S Velichko

Publications and source records attributed to Y S Velichko.

4 recordsLinked to original sources

PubMed2006

Electrostatic attraction between cationic-anionic assemblies with surface compositional heterogeneities.

Electrostatics play a key role in biomolecular assembly. Oppositely charged biomolecules, for instance, can be coassembled into functional units, such as DNA and histone proteins into nucleosomes and actin-binding protein complexes into cytoskeleton components, at appropriate ionic conditions. These cationic-anionic coassemblies often have surface charge heterogeneities that result from the delicate balance between electrostatics and packing constraints. Despite their importance, the precise role of surface charge heterogeneities in the organization of cationic-anionic coassemblies is not well understood. We show here that coassemblies with charge heterogeneities strongly interact through polarization of the domains. We find that this leads to symmetry breaking, which is important for functional capabilities, and structural changes, which is crucial in the organization of coassemblies. We determine the range and strength of the attraction as a function of the competition between the steric and hydrophobic constraints and electrostatic interactions.

Anions↗

PubMed2005

Pattern formation on the surface of cationic-anionic cylindrical aggregates.

Charged pattern formation on the surfaces of self-assembled cylindrical micelles formed from oppositely charged heterogeneous molecules such as cationic and anionic peptide amphiphiles is investigated. The net incompatibility chi among different components results in the formation of segregated domains, whose growth is inhibited by electrostatics. The transition to striped phases proceeds through an intermediate structure governed by fluctuations, followed by states with various lamellar orientations, which depend on cylinder radius Rc and chi. We analyze the specific heat, susceptibility S(q*), domain size Lambda = 2pi/q*, and morphology as a function of Rc and chi.

Anions↗

PubMed2001

Self-assembled pearling structure of long duplex DNA with histone H1.

We report that complexes of giant DNA molecules with histone H1 proteins form a pearl necklace-like structure when the complexes are prepared by natural dilution from a high-salt solution (2 M NaCl) to a low-salt solution (0.2 M and 50 mM NaCl). We performed real-time observations on the conformational changes of individual T4 phage DNA (166 kb) molecules in bulk solution by fluorescence microscopy. To identify H1-binding regions on individual DNA molecules, we also performed immunofluorescence microscopic observations on the DNA-H1 complex spread on a glass surface. It was found that histone H1 binds DNA in a highly co-operative manner and is accompanied by local folding of the DNA. On the basis of the experimental observations and a theoretical simulation, we propose a self-assembling mechanism for the pearling structure.

Bacteriophage T4↗

PubMed2000

Surface-induced DNA superhelicity.

Certain biopolymers, such as DNA, have a double-stranded twisted structure and frequently exhibit a supercoiled conformation. Over the past decade, extensive conformational analyses of different biopolymers have been performed using atomic force microscopy. In this technique, a necessary step in sample preparation is the adsorption of molecules on the surface, which could affect the chain conformation. Using a Monte Carlo simulation, we studied the adsorption process of circular semiflexible twisted double-stranded polymer chains on a solid surface with an emphasis on the conformational properties. We found that the conformation of an adsorbed chain strongly depends on the number of double-helical turns of the chain. Chains with weak twisting adsorbed on the surface assumes higher superhelical twisting, whereas the coiled state is seen in the bulk solution. After the adsorption, double-helical turns are accumulated in the adsorbed ("train") sections giving more conformational freedom to the nonadsorbed ("loop") sections. Chains with strong twisting show small conformational changes with adsorption. In both cases, superhelicity shows the opposite sign of writhing.

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