Dendrimers are synthetic, highly branched, spherical macromolecules with nanometer dimensions and potential applications in DNA and drug delivery systems. Human serum albumin (HSA) is a major transporter for delivering several endogenous compounds and drugs in vivo. The aim of this study was to examine the interaction of human serum albumin with several dendrimers such as mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions, using constant protein concentration and various dendrimer compositions. FTIR, UV-visible, CD, and fluorescence spectroscopic methods were used to analyze macromolecule binding mode, the binding constant and the effects of dendrimers complexation on HSA stability and conformation. Structural analysis showed that dendrimers bind HSA via polypeptide polar groups (hydrophilic) with number of bound polymer (n) 1.08 (mPEG-PAMAM-G3), 1.50 (mPEG-PAMAM-G4), and 0.96 (PAMAM-G4). The overall binding constants estimated were of KmPEG-G3=1.3 (+/-0.2)x10(4) M(-1), KmPEG-G4=2.2 (+/-0.4)x10(4) M(-1), and KPAMAM-G4=2.6 (+/-0.5)x10(4) M(-1). HSA conformation was altered by dendrimers with a major reduction of alpha-helix and increase in random coil and turn structures suggesting a partial protein unfolding.

We report the complexation of bovine serum albumin (BSA) with several dendrimers of different compositions mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions using constant protein concentration and various dendrimer contents. FTIR, CD, and fluorescence spectroscopic methods were used to analyze polymer binding mode, the binding constant, and the effects of dendrimer complexation on BSA stability and conformation. Structural analysis showed that dendrimers bind BSA via hydrophilic and hydrophobic interactions with a number of bound polymers (n): 1.30 for mPEG-PAMAM-G3, 1.30 for mPEG-PAMAM-G4, and 1.0 for PAMAM-G4. The polymer-BSA binding constants were K(mPEG-G3) = 5.0 (+/-0.8) x 10(3) M(-1), K(mPEG-G4) = 1.0 (+/-0.3) x 10(4) M(-1), and K(PAMAM-G4) = 1.1 (+/-0.4) x 10(4) M(-1). Dendrimer binding altered BSA conformation with a major reduction of alpha-helix and an increase in random coil and turn structures, indicating a partial protein unfolding.

Dendrimers are unique synthetic macromolecules of nanometer dimensions with a highly branched structure and globular shape. Among dendrimers, polyamidoamine (PAMAM) have received most attention as potential transfection agents for gene delivery, because these macromolecules bind DNA at physiological pH. The aim of this study was to examine the interaction of calf-thymus DNA with several dendrimers of different compositions, such as mPEG-PAMAM (G3), mPEG-PAMAM (G4), and PAMAM (G4) at physiological conditions, using constant DNA concentration and various dendrimer contents. FTIR, UV-visible, and CD spectroscopic methods, as well as atomic force microscopy (AFM), were used to analyze the macromolecule binding mode, the binding constant, and the effects of dendrimer complexation on DNA stability, aggregation, condensation, and conformation. Structural analysis showed a strong dendrimer-DNA interaction via major and minor grooves and the backbone phosphate group with overall binding constants of K(mPEG-G3) = 1.5 (±0.5) × 10(3) M(-1), K(mPEG-G4) = 3.4 (±0.80) × 10(3) M(-1), and K(PAMAM-G4) = 8.2 (±0.90) × 10(4) M(-1). The order of stability of polymer-DNA complexation is PAMAM-G4 > mPEG-G4 > mPEG-G3. Both hydrophilic and hydrophobic interactions were observed for dendrimer-DNA complexes. DNA remained in the B-family structure, while biopolymer particle formation and condensation occurred at high dendrimer concentrations.