Complexation between DNA and Peptides with Precisely Controlled Charge Density and Distribution

Using three designed peptides with precisely-controlled charge density and three types of DNAs with different length and flexibility, the effect of charge density on the formation of PEC was studied. Highly charged (KKKK)5 interacts strongly with 21 bp dsDNA to form large complex, followed by precipitation; while the medium charged (KGKG)5 only form complex with 21 bp dsDNA at proper +/− charge ratios; and no prominent complex between weakly charged (KGGG)5 and 21 bp dsDNA is observed at the same conditions. Similar trend is observed when the peptides form complex with 2000 bp DNA or 21nt ssDNA. It is also found that the complex formed by adding peptide to DNA is in random coil conformation, but the complex prepared by the inverse order is in molten globule state. Re-dissolution of the complex occurs only when DNA is added to peptides with similar or shorter length.