Electrostatic Selectivity in Protein鈥揘anoparticle Interactions
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- 作者：Kaimin Chen ; Yisheng Xu ; Subinoy Rana ; Oscar R. Miranda ; Paul L. Dubin ; Vincent M. Rotello ; Lianhong Sun ; Xuhong Guo
- 刊名：Biomacromolecules
- 出版年：2011
- 出版时间：July 11, 2011
- 年：2011
- 卷：12
- 期：7
- 页码：2552-2561
- 全文大小：1092K
- 年卷期：v.12,no.7(July 11, 2011)
- ISSN：1526-4602
文摘
The binding of bovine serum albumin (BSA) and 尾-lactoglobulin (BLG) to TTMA (a cationic gold nanoparticle coupled to 3,6,9,12-tetraoxatricosan-1-aminium, 23-mercapto-N,N,N-trimethyl) was studied by high-resolution turbidimetry (to observe a critical pH for binding), dynamic light scattering (to monitor particle growth), and isothermal titration calorimetry (to measure binding energetics), all as a function of pH and ionic strength. Distinctively higher affinities observed for BLG versus BSA, despite the lower pI of the latter, were explained in terms of their different charge anisotropies, namely, the negative charge patch of BLG. To confirm this effect, we studied two isoforms of BLG that differ in only two amino acids. Significantly stronger binding to BLGA could be attributed to the presence of the additional aspartates in the negative charge domain for the BLG dimer, best portrayed in DelPhi. This selectivity decreases at low ionic strength, at which both isoforms bind well below pI. Selectivity increases with ionic strength for BLG versus BSA, which binds above pI. This result points to the diminished role of long-range repulsions for binding above pI. Dynamic light scattering reveals a tendency for higher-order aggregation for TTMA鈥揃SA at pH above the pI of BSA, due to its ability to bridge nanoparticles. In contrast, soluble BLG鈥揟TMA complexes were stable over a range of pH because the charge anisotropy of this protein at makes it unable to bridge nanoparticles. Finally, isothermal titration calorimetry shows endoenthalpic binding for all proteins: the higher affinity of TTMA for BLGA versus BLGB comes from a difference in the dominant entropy term.