Contribution of Hydrophobicity to Thermodynamics of Ligand-DNA Binding and DNA Collapse

Abstract

The importance of understanding the dynamics of DNA condensation is inherent in the biological significance of DNA packaging in cell nuclei, as well as for gene therapy applications. Specifically, the role of ligand hydrophobicity in DNA condensation has received little attention. Considering that only multivalent cations can induce true DNA condensation, previous studies exploring monovalent lipids have been unable to address this question. In this study we have elucidated the contribution of the hydrophobic effect to multivalent cation- and cationic lipid-DNA binding and DNA collapse by studying the thermodynamics of cobalt hexammine-, spermine-, and lipospermine-plasmid DNA binding at different temperatures. Comparable molar heat capacity changes (DeltaC(p)) associated with cobalt hexammine- and spermine-DNA binding (-23.39 cal/mol K and -17.98 cal/mol K, respectively) suggest that upon binding to DNA, there are insignificant changes in the hydration state of the methylene groups in spermine. In contrast, the acyl chain contribution to the DeltaC(p) of lipospermine-DNA binding (DeltaC(p ) = DeltaC(p lipospermine) - DeltaC(p spermine)) is significant (-220.94 cal/mol K). Although lipopermine induces DNA ordering into "tubular" suprastructures, such structures do not assume toroidal dimensions as observed for spermine-DNA complexes. We postulate that a steric barrier posed by the acyl chains in lipospermine precludes packaging of DNA into dimensions comparable to those found in nature.

Fatty acid–spermine conjugates as DNA carriers for nonviral in vivo gene delivery

“…In all clear and transparent preparations, intensity values resulting from Fatty acid-spermine conjugates as DNA carriers JR Viola et al light scattered by particles with diameters larger than 1 mm were neglected, as this light scatter most probably results from dust particles. 18,23 Most of the formulations presented a relatively broad population distribution, except for decanoylspermine/DNA 1:1 ( Figure 5). An increase in the concentration of butanoylspermine in the formulation of DNA complexes resulted in the formation of more stable colloidal solutions, as evidenced by a decrease in the average particle diameter, together with an increase in light intensity ( Figure 5).…”

“…Polyamines have been extensively used for the development of nonviral vectors and this includes studies in which lipospermines typically either contain double or have longer hydrocarbon chains. 18,21,[28][29][30][31] It has previously been suggested that DNA-binding affinity is a function of both charge and hydrophobicity. 19,32 However, to what degree this affinity is beneficial for gene delivery is not clear.…”

“…Previous studies with a chemically different set of spermine derivatives used for DNA condensation have shown the formation of complexes, but not as well defined or with as regular a shape as some of the DNA particles shown in this investigation, particularly with decanoylspermine/DNA. 18,34 Influence of imaging techniques on morphological characterization of DNA complexes does not seem to be uncommon and cryo-EM emerges as that which may interfere the least. [24][25][26][27]35 The morphology of these lipospermines is likely to influence their in vivo transfection efficiency, but the correlation is not clear.…”

“…17 DNA binding by the condensing agent can be improved either by increasing the charge density of the positively charged molecule or by introducing hydrophobic contributions. 18,19 Thus, the attachment of a short lipidic tail to spermine could potentially improve the binding of this molecule to DNA and thereby affect its ability to protect DNA on condensation. Geall and Blagbrough 19 showed the binding affinity between plasmid DNA (pDNA) and oleic and palmitic lipospermines.…”

Sequence and length dependent thermodynamic differences in heterocyclic diamidine interactions at AT base pairs in the DNA minor groove

“…Similarly, the observed binding enthalpy can be parsed into two contributions: (3) whereΔH pe is assumed to be essentially zero [53], and ΔH t equal to ΔH obs . For poly(dA)·poly (dT) binding with DB75, ΔH t was obtained as 3.1 kcal mol −1 , while for poly(dA-dT)·poly(dAdT) binding with DB75, ΔH t was obtained as −4.5 kcal mol −1 .…”