On the Mechanism of Bioinspired Formation of Inorganic Oxides: Structural Evidence of the Electrostatic Nature of the Interaction between a Mononuclear Inorganic Precursor and Lysozyme

Abstract

Nature has evolved several molecular machineries to promote the formation at physiological conditions of inorganic materials, which would otherwise be formed in extreme conditions. The molecular determinants of this process have been established over the last decade, identifying a strong role of electrostatics in the first steps of the precipitation. However, no conclusive, structure-based evidence has been provided so far. In this manuscript, we test the binding of lysozyme with silica and titania potential precursors. In contrast with the absence of structural information about the interaction with the silica precursor, we observe the interaction with a mononuclear titanium(IV) species, which is found to occur in a region rich of positive charges.

Lysozyme is Sterically Trapped Within the Silica Cage in Bioinspired Silica–Lysozyme Composites: A Multi-Technique Understanding of Elusive Protein–Material Interactions

“… 12 However, no such interaction could be observed for silicic acid. 12 A recent study suggests that liquid–liquid phase separation (LLPS) is responsible for driving the polymerization; however, the LLPS is related to overall charge, 13 and there are reports that lysozyme tends not to undergo LLPS at pH values around 7. 14 It has been previously demonstrated that lysozyme catalyzes the silica colloid formation from silicon alkoxide solutions and dilute water glass solutions around neutral pH.…”

“… 17 However, no evidence of structural distortion has been observed by solution nuclear magnetic resonance (NMR) spectroscopy. 12 …”

“…17 However, no evidence of structural distortion has been observed by solution nuclear magnetic resonance (NMR) spectroscopy. 12 Lysozyme is often used as a model for interface interactions because it is easily obtainable, has intriguing biophysical properties (often proteins are negative, rather than positive 18 ), and has a useful antimicrobial activity. 19−24 Therefore, it is expected that an improved understanding of lysozyme− material interactions could provide hints for applications beyond the study of bioinspired mineralization.…”

“…The reactivity of lysozyme, which is common to other highly positively charged proteins and polypeptides, is reasonably attributable to electrostatic interactions, which involve the positively charged side chains of lysozyme and the negatively charged monosilicic acid, oligomeric silica, and colloidal silica. Indeed, a recent crystal structure localized a hydrolyzed species of the titanium precursor at a positive patch on the protein surface . However, no such interaction could be observed for silicic acid .…”

“…Indeed, a recent crystal structure localized a hydrolyzed species of the titanium precursor at a positive patch on the protein surface . However, no such interaction could be observed for silicic acid . A recent study suggests that liquid–liquid phase separation (LLPS) is responsible for driving the polymerization; however, the LLPS is related to overall charge, and there are reports that lysozyme tends not to undergo LLPS at pH values around 7 .…”