Structure and Function of Hemoglobin Confined Inside Silica Nanotubes

Abstract

Investigations on the structure and function of hemoglobin (Hb) confined inside sol-gel template synthesized silica nanotubes (SNTs) have been discussed here. Immobilization of hemoglobin inside SNTs resulted in the enhancement of direct electron transfer during an electrochemical reaction. Extent of influence of nanoconfinement on protein activity is further probed via ligand binding and thermal stability studies. Electrochemical investigations show reversible binding of n-donor liquid ligands, such as pyridine and its derivatives, and predictive variation in their redox potentials suggests an absence of any adverse effect on the structure and function of Hb confined inside nanometer-sized channels of SNTs. Immobilization also resulted in enhanced thermal stability of Hb. The melting or denaturation temperature of Hb immobilized inside SNTs increase by approximately 4 degrees C as compared with that of free Hb in solution.

Templated-assisted one-dimensional silica nanotubes: synthesis and applications

“…109 Higher drug yields could be obtained when impulses of shorter duration and shorter time intervals between successive impulses were employed. 108 The influence of confinement on the ligand binding activity of hemoglobin was studied systematically and the results suggested that the immobilization of hemoglobin inside silica nanotubes didn't result in any distortion of the native protein structure and function.…”

Immobilization of Proteins in Silica Gel: Biochemical and Biophysical Properties

“…The templating effect of the embedded biomolecules during gel polymerization could explain the formation of pores that fit the size and shape of the encapsulated molecules; this would pose steric constraints to highly expanded denatured states or unfolding transition states, resulting in thermodynamic stabilization of native states and faster folding rates [62]. Caging and excluded volume effects on polymer dynamics and the relevance for the stability of encapsulated proteins have been the subject of a large theoretical, computational and experimental effort in recent years [62][63][64][65][66][67][68][69][70][71][72][73][74]. Electrostatic interactions between charged or polar amino acid side chains and the pore surface, that is negatively charged at nearphysiological pH (the isoelectric point can be as low as 2.1 [75]), could also be a factor affecting stability [76,77].…”

“…Hemoglobin and myoglobin were also used as test molecules to investigate the effects of encapsulation on protein stability and folding [71,[97][98][99]. However, the most striking result about Hb encapsulated in silica gels is the perfect conservation of equilibrium oxygen binding properties observed in solution under comparable conditions [54,57,58,82,100,101] (Fig.…”

Hemoglobin Dynamics in Solution vis-à-vis Under Confinement: An Electrochemical Perspective

“…The double-layer thickness is characterized by the Debye length, which is inversely proportional to the ionic strength of the medium . Confinement as an efficient tool for enhancing electrochemical response from heme proteins has been well established in the literature from our group and the structural features observed under confinement have also been studied in detail. − In this paper, we use a combination of experimental techniques probing different time scales to assess the dynamic features of the heme protein hemoglobin under confinement. We use the observed changes in protein dynamics under confinement to explain the electrochemical response observed under confinement.…”