title: Chemistry of conjugation to gold nanoparticles affects G-protein activity differently.
abstract: BACKGROUND
  Gold nanoparticles (AuNP) are extensively used as biophysical tools in the area of medicine and technology due to their distinct properties. However, vivid understanding of the consequences of biomolecule-nanomaterial interactions is still lacking. In this context, we explore the affect of conjugation of Gαi1 subunit (of heterotrimeric G-proteins) to AuNP and examine its consequences. We consider two bio-conjugation strategies covalent and non-covalent binding.
  
  
  RESULTS
  Affinity of the AuNP to the Gαi1 is 7.58 × 10 12 M-1. AuNP conjugated Gαi1 exhibits altered kinetics of activation, non-covalent bio-conjugates displays retarded kinetics, up to 0.88 fold when GTPγS was used as ligand, of protein activation contrary to covalent conjugates which accelerates it to ~ 5 fold. Conjugation influence intrinsic Gαi1 GTPase function in conflicting modes. Non-covalent conjugation inhibits GTPase function (decrease in activity upto 0.8 fold) whilst covalent conjugation drastically accelerates it (12 fold increase in activity). Altered basal nucleotide uptake in both types of conjugates and GTPase function in non-covalent conjugate are almost comparable except for GTPase property of covalent conjugate. The effect is despite the fact that conjugation does not change global conformation of the protein.
  
  
  CONCLUSIONS
  These findings provide clear evidence that nanoparticles, in addition to 'passive interaction' with protein (biomolecule), can interact "actively" with biomolecule and modify its function. This concept should be considered while engineering nanoparticle based delivery systems in medicine.
authors.affiliation: Department of Biotechnology, Indian Institute of Technology Madras, Chennai, 600036, India.
authors.forename: Vibha
authors.initials: V
authors.lastname: Singh
authors.forename: Santhosh P Nagappan
authors.initials: SP
authors.lastname: Nair
authors.forename: Gopala Krishna
authors.initials: GK
authors.lastname: Aradhyam
mesh_terms: D000818:Animals; D002942:Circular Dichroism; D006046:Gold / Q000032:analysis / Q000737:chemistry*; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry*; D007700:Kinetics; D053768:Metal Nanoparticles / Q000032:analysis / Q000737:chemistry*; D009711:Nucleotides / Q000378:metabolism; D011487:Protein Conformation; D051381:Rats; D013050:Spectrometry, Fluorescence; D008063:Thioctic Acid / Q000031:analogs & derivatives / Q000032:analysis / Q000737:chemistry
chemical_list: D009711:Nucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008063:Thioctic Acid; D006046:Gold; C015144:dihydrolipoic acid; D020962:Heterotrimeric GTP-Binding Proteins