Related Experiment Video
Updated: Jul 19, 2026
06:48
CD Spectroscopy to Study DNA-Protein Interactions
Published on: February 10, 2022
Solubility and charge inversion of complexes of DNA and basic proteins
Eric Raspaud1, J Pelta, M de Frutos
1Laboratoire de Physique des Solides, CNRS UMR 8502, Université Paris Sud, 91405 Orsay Cedex, France. raspaud@lps.u-psud.fr
Physical Review Letters
|October 10, 2006
Summary
Basic proteins like protamines and histones condense DNA. In vitro studies show these proteins form soluble complexes with DNA and PSS within a narrow charge ratio, with charge inversion observed.
Area of Science:
- Biochemistry
- Molecular Biology
- Biophysics
Background:
- Protamines and histones H1 are basic proteins known for in vivo DNA condensation.
- Understanding DNA-protein interactions is crucial for molecular biology and gene regulation.
Purpose of the Study:
- To investigate the in vitro condensation and solubilization of linear DNA by basic proteins (protamines, histones H1) and a synthetic polyanion (PSS).
- To determine the effect of charge concentration ratio on complex formation at low ionic strength.
Main Methods:
- In vitro complexation experiments using linear DNA, protamines, histones H1, and Poly(Styrene-Sulfonate) (PSS).
- Varying the charge concentration ratio to observe phase separation and complex formation.
- Analysis of complex properties including solubility and charge.
Main Results:
- Phase separation occurred within a narrow charge ratio range for short DNA and PSS, forming polydisperse, charged complexes with detected charge inversion.
- Long DNA chains formed complexes that were insoluble in excess proteins.
- Complexation behavior is highly dependent on DNA length and charge ratio.
Conclusions:
- Basic proteins can condense DNA in vitro, but complex formation and solubility are sensitive to DNA length and charge ratio.
- The findings provide insights into the mechanisms of DNA condensation and the formation of protein-DNA complexes.
Related Concept Videos
03:45Formation of Complex Ions
A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...
01:03Single-Strand DNA Binding Proteins
For successful DNA replication, the unwinding of double-stranded DNA must be accompanied by stabilization and protection of the separated single strands of the DNA. This crucial task is performed by single-strand DNA-binding (SSB) proteins. They bind to the DNA in a sequence-independent manner, which means that the nitrogenous bases of the DNA need not be present in a specific order for binding of SSB proteins to it. The binding of SSB proteins straightens single-stranded DNA (ssDNA) and makes...
01:09Complexation Equilibria: Factors Influencing Stability of Complexes
In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
00:55DNA Helicases
DNA unwinding helicase enzymes are a type of motor protein. Motor proteins can translocate along filaments or polymers using energy generated from ATP hydrolysis. Helicases are involved in all the important cellular processes where DNA unwinding is required, such as DNA replication, repair, recombination, and transcription. They are present in all living organisms, but vary in their structure, function, and mechanism of action. For example, in prokaryotes, DnaB helicase binds and translocates...
01:22EDTA: Chemistry and Properties
Polydentate ligands are most widely used in complexometric titrations because they form more stable complexes with the metal ions than mono- or bidentate ligands due to the chelate effect. Examples of polydentate ligands are ethylenediaminetetraacetic acid (EDTA), crown ethers, and cryptands. The most important feature of optimal polydentate ligands is the ability to form 1:1 complexes in a single-step process. Amino carboxylic acid derivatives are frequently used as complexing agents. EDTA is...
02:02DNA Topoisomerases
Topoisomerases are enzymes that relax overwound DNA molecules during various cell processes, including DNA replication and transcription. These enzymes regulate positive and negative DNA supercoiling without changing the nucleotide sequence. DNA overwinding in a clockwise direction results in positively supercoiled DNA, whereas underwinding in a counterclockwise direction produces negatively supercoiled DNA.
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...
Types and Mechanism of action
Topoisomerases are divided into two main types. Type I...