title: Unfolding and inactivation of proteins by counterions in protein-nanoparticles interaction.
abstract: In this work, the structure and activity of proteins; such as, hen egg lysozyme (HEWL) and calf intestine alkaline phosphatase (CIAP); have been investigated after incubation with surface coated iron oxide nanoparticles (IONPs) in water. IONPs were coated with counterions bound charge-ligands and were named as the charge-ligand counterions iron oxide nanoparticles (CLC-IONPs). The coating was done with tri-lithium citrate (TLC) and tri-potassium citrate (TKC) to have negative surface charge of CLC-IONPs and Li(+) and K(+), respectively, as counterions. To have positive surface charge, IONPs were coated with cetylpyridinium chloride (CPC) and cetylpyridinium iodide (CPI) having Cl(-) and I(-), respectively, as counterions. The secondary structure of proteins was measured using far ultraviolet circular dichroism (CD) spectroscopy which showed that both proteins were irreversibly unfolded after incubation with CLC-IONPs. The unfolded proteins were seen to be functionally inactive, as confirmed through their activity assays, i.e., HEWL with Escherichia coli (E. coli) and CIAP with para-nitrophenyl phosphate (pNPP). Additionally, we have observed that monomeric hemoglobin (Hb) from radio-resistant insect Chironomus ramosus (ChHb) was also partially unfolded upon interaction with CLC-IONPs. This work clearly shows the role of counterions in protein inactivation via protein-nanoparticles interaction and, therefore, CLC-IONPs could be used for therapeutic purpose.
authors.affiliation: UGC-DAE Consortium for Scientific Research, Mumbai Centre, Mumbai 400085, India. Electronic address: ghoshg@csr.res.in.
authors.forename: Goutam
authors.initials: G
authors.lastname: Ghosh
authors.affiliation: Department of Zoology, Savitribai Phule Pune University, Ganeshkhind, Pune 411007, India.
authors.forename: Pallavi S
authors.initials: PS
authors.lastname: Gaikwad
authors.affiliation: Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Lata
authors.initials: L
authors.lastname: Panicker
authors.affiliation: Department of Zoology, Savitribai Phule Pune University, Ganeshkhind, Pune 411007, India.
authors.forename: Bimalendu B
authors.initials: BB
authors.lastname: Nath
authors.affiliation: Molecular Biology Division, Bhabha Atomic Research Centre, Mumbai 400085, India. Electronic address: ritam@barc.gov.in.
authors.forename: Rita
authors.initials: R
authors.lastname: Mukhopadhyaya
mesh_terms: D000469:Alkaline Phosphatase / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002645:Chickens; D002942:Circular Dichroism; D000067493:Dynamic Light Scattering; D005290:Ferric Compounds / Q000737:chemistry; D057446:Hydrodynamics; D007477:Ions; D008024:Ligands; D009113:Muramidase / Q000737:chemistry / Q000378:metabolism*; D053758:Nanoparticles / Q000737:chemistry*; D009596:Nitrophenols / Q000737:chemistry / Q000378:metabolism; D058767:Protein Unfolding; D055672:Static Electricity
chemical_list: D005290:Ferric Compounds; D007477:Ions; D008024:Ligands; D009596:Nitrophenols; C000499:ferric oxide; C024719:4-nitrophenyl; D000469:Alkaline Phosphatase; C421864:hen egg lysozyme; D009113:Muramidase
keywords: Bioassay; Circular dichroism; Functional iron oxide nanoparticles; Optical density; Protein’s secondary structure; Structure-function relationship of proteins