Properties of Human Serum Albumin Entrapped in Sol−Gel-Derived Silica Bearing Covalently Tethered Sugars

Abstract

Silica derived from biocompatible silane precursors and containing covalently bound sugar moieties has recently been reported to be a much more biocompatible matrix for protein entrapment than any previously synthesized materials. To better understand the nature of these new materials, the steady-state and time-resolved fluorescence of human serum albumin (HSA) was used to examine the conformation, dynamics, accessibility, thermal stability, and degree of ligand binding after entrapment of the protein into sol−gel-processed glasses derived from either tetraethyl orthosilicate (TEOS) or diglycerylsilane (DGS), which in some cases contained covalently bound gluconamidylsilane (GLS) moieties. It was observed that the initial conformation, accessibility to external analytes, thermal stability, long-term stability, and degree of ligand binding to HSA were best in DGS-derived materials that contained covalently tethered GLS relative to unmodified DGS-derived materials, TEOS, or TEOS/GLS-derived materials. Measurement of protein rotational dynamics showed that entrapment led to an immediate loss of global motion in all materials. However, the restriction of motion was most dramatic in GLS-doped materials, suggesting preferential interactions of the protein with the sugar-coated surfaces. As aging proceeded, both protein dynamics and the degree of ligand binding decreased, with a gradual loss of segmental motion and a significant increase in local motion in the vicinity of the probe, consistent with unfolding and surface adsorption of the protein, leading to loss of function. Overall, our findings suggest that the use of a biocompatible precursor (DGS) and the addition of a covalently bound sugar both contribute to improved protein performance. However, of these two the use of a biocompatible precursor is the most important factor, and in such cases addition of sugars further improves protein performance. In contrast, the use of the sugar-based additive with a nonbiocompatible precursor such as TEOS imparted essentially no benefit, demonstrating the importance of biocompatible processing conditions.

Favourable influence of hydrophobic surfaces on protein structure in porous organically-modified silica glasses

“…Some of the common hydrophilic substitutions include glasses modified with aminopropyl [48][49][50][51], carboxyethyl [48,49], glycidoxypropyl [50,51], and diglyceryl or gluconamidyl groups [52][53][54]. Of special interest with regard to hydrophilic organically-modified glasses, Ackerman and co-workers have reported outstanding enzyme activities following protein adsorption into functionalized mesoporous silica prepared using a non-ionic block copolymer surfactant as the template [48,49].…”

“…In addition to apoMb, enhanced conformational stability at elevated temperatures has been observed for many glass-entrapped proteins including α-lactalbumin [22], lysozyme [22,24], human serum albumin [24,26,54], creatine kinase [31], monellin [59], oncomodulin [64], cytochrome c [65], and carbonic anhydrase [66]. The outstanding thermal stability of proteins in organically-modified glasses, as demonstrated here for apoMb, bodes well for the use of such biomaterials in industry, including the development of new nanobiodevices [6,27].…”

Mesostructured Silica for Optical Functionality, Nanomachines, and Drug Delivery

“…As a result, a number of approaches have emerged in recent years that greatly lower the alcohol content and generally provide improvements in microstructure control. These include aqueous synthesis routes based on sodium silicate, 26 and the use of biocompatible silane precursors containing bound sugar moieties 27…”

Enzyme‐Based Bioinorganic Materials

“…Ballesteros et al describe a method to surmount the problem of alcohol release during the alkoxide hydrolysis by using more biocompatible precursors such as poly(glycerylsilicate) which liberate bioprotective alcohols (i.e., glycerol) after auto-hydrolysis [157]. Other silicas derived from more biocompatible precursors [158,159] (i.e., diglyceryl silane, gluconamidylsilane) have been proposed by Brennan et al Such sol-gel precursors lead to highly porous bio-hybrid materials with activities approaching those of the free enzyme.…”