The Effect of Molecular Crowding on the Stability of Human c-MYC Promoter Sequence I-Motif at Neutral pH

Molecules

Jingjing Cui¹  Phillip Waltman¹  Vu H. Le¹ 

[1] id="af1-molecules-18-12751">Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, U

关键词: i-motif;    stability;    neutral pH;    molecular crowding;    excluded volume effect;   

DOI  :  10.3390/molecules181012751

来源: mdpi

【 摘 要 】

We have previously shown that c-MYC promoter sequences can form stable i-motifs in acidic solution (pH 4.5–5.5). In terms of drug targeting, the question is whether c-MYC promoter sequence i-motifs will exist in the nucleus at neutral pH. In this work, we have investigated the stability of a mutant c-MYC i-motif in solutions containing a molecular crowding agent. The crowded nuclear environment was modeled by the addition of up to 40% w/w polyethylene glycols having molecular weights up to 12,000 g/mol. CD and DSC were used to establish the presence and stability of c-MYC i-motifs in buffer solutions over the pH range 4 to 7. We have shown that the c-MYC i-motif can exist as a stable structure at pH values as high as 6.7 in crowded solutions. Generic dielectric constant effects, e.g., a shift in the pKa of cytosine by more than 2 units (e.g., 4.8 to 7.0), or the formation of non-specific PEG/DNA complexes appear to contribute insignificantly to i-motif stabilization. Molecular crowding, largely an excluded volume effect of added PEG, having a molecular weight in excess of 1,000 g/mol, appears to be responsible for stabilizing the more compact i-motif over the random coil at higher pH values.

【 授权许可】

CC BY   
© 2013 by the authors; licensee MDPI, Basel, Switzerland.