Probing Surface Properties of Cytochrome c at Au Bionanoconjugates

Abstract

Bionanoconjugates were created with cytochrome c from horse heart (HCc) or yeast (YCc) and citrate-stabilized gold nanoparticles (AuNPs). Evidence for the formation of stable HCc-AuNP and YCc-AuNP bionanoconjugates came from a 5 nm red-shift of the surface plasmon resonance band of the AuNPs, increase of the -potential, and direct visualization by atomic force microscopy. Langmuir isotherm fittings of -potential data indicated that higher enthalpy changes are involved in the formation of the HCc-AuNP than in YCc-AuNP. UV-vis and circular dichroism studies of pH-induced aggregation of the bionanoconjugates revealed distinct protonation patterns with an aggregation pH of 8.8 and 6.2 for YCc-AuNP and HCc-AuNP, respectively. No appreciable changes were observed in the secondary structure of HCc in HCc-AuNP. In contrast, YCc in YCc-AuNP presented a decrease in R-helix content upon AuNP binding and an increase in -sheet content upon pH-induced aggregation. Data discussion is based on the distinct binding modes of both proteins to the AuNPs via a covalent bond (Cys 102) for YCc and via electrostatic interaction for HCc.

Bionanoconjugates of tyrosinase and peptide-derivatised gold nanoparticles for biosensing of phenolic compounds

“…Since surface potential is associated to the surface charge and the thickness of the double layer, the adsorption of protein will alter these parameters. As reported previously (Brewer et al 2005;Gomes et al 2008), it is expected that an increasing amount of protein bound to the nanoparticle surface will lead to a shift in the surface potential until a stable value is observed, indicating the nanoparticle surface is saturated with protein.…”

“…2). The AuNPs:CALNN alone presented a f-potential of -47.7 ± 0.3 mV, a value marginally higher than that obtained for citrate-stabilised AuNPs (Brewer et al 2005;Gomes et al 2008). The f-potential of the free enzyme in the same conditions (pH 7.0 and 25°C) was -17.5 ± 0.5 mV.…”

“…The effective conjugation of proteins and AuNPs has been demonstrated for different proteins, including albumin (BSA) and Cytochrome c (Brewer et al 2005;Gomes et al 2008). The formation of BNCs was supported by the 3-nm red-shift to 525 nm observed in the plasmon resonance band of the BNCs relative to the functionalised AuNPs alone.…”

Effect of surface coating on the biodistribution profile of gold nanoparticles in the rat

“…It could be related to differences in stability and/or interaction with serum proteins between bare and peptide-coated AuNPs. In fact, we have previously reported that the affinity of proteins to Cit-AuNPs and to AuNPs with thiol-ligands (peptides with a terminal Cys or other organic molecules) is different, despite the fact that the functional groups at the outer-surface of the AuNPs were in both cases carboxylates [40]. Although changes in the peptide sequence could affect the stability and modify NPs interactions with biomolecules [41], no major differences were observed among the three pentapeptidefunctionalized AuNPs employed in our study.…”

Colorimetric Determination of pH Values using Silver Nanoparticles Conjugated with Cytochrome c

“…This red-shift between bare AgNPs and Cyt c-AgNP probes is related to alterations in the refractive index of AgNPs by the Cyt c layer. 21 The peak FWHM for the conjugates at pH 9.5 was relatively broadened to 123 nm, indicating that aggregates were formed by Cyt c absorbed on the Ag surface during the conjugation process. As the pH of the solution was decreased, the absorbance peak at 401 nm disappeared and a broad peak appeared newly in the range between 500 nm and 750 nm.…”