Role of Sporopollenin Shell Interfacial Properties in Protein Adsorption

Abstract

Sporopollenin shells isolated from natural pollen grains have received attention in translational and applied research in diverse fields of drug delivery, vaccine delivery, and wastewater remediation. However, little is known about the sporopollenin shell's potential as an adsorbent. Herein, we have isolated sporopollenin shells from four structurally diverse pollen species, black walnut, marsh elder, mugwort, and silver birch, to study protein adsorption onto sporopollenin shells. We investigated three major interfacial properties, surface area, surface functional groups, and surface charge, to elucidate the mechanism of protein adsorption onto sporopollenin shells. We showed that sporopollenin shells have a moderate specific surface area (<12 m 2 /g). Phosphoric acid and potassium hydroxide treatments that were used to isolate sporopollenin shells from natural pollen grains also result in the functionalization of sporopollenin shell surfaces with ionizable groups of carboxylic acid and carboxylate salt. As a result, sporopollenin shells exhibit a negative ζ potential in the range of −75 to −82 mV at pH 10 when dispersed in water. The ζ potentials of sporopollenin shells remain negative in the pH range of 2.5−11, with the absolute value of ζ potential showing a decrease with the decrease in pH. The negative surface charge promotes the adsorption of protein onto the sporopollenin shell via electrostatic interaction. Despite having a moderate surface area, sporopollenin shells adsorb a significant amount of lysozyme (145−340 μg lysozyme per mg of sporopollenin shells). Lysozyme adsorption onto sporopollenin shells alters the surface, and the surface charge becomes positive at acidic pH. Overall, this study demonstrates the potential of sporopollenin shells to adsorb proteins, highlights the critical role of sporopollenin shell's interfacial properties in protein adsorption, and identifies the mechanism of protein adsorption on sporopollenin shells.

First Cu-Nanostar as Sustainable Catalyst Realized through Synergistic Effects of Bowl-shaped Features and Surface Activation of Sporopollenin Exine

“…Because of its unique features, such as cytocompatibility, 35 large cavities for drug cargo, and a tough protecting layer, SP is being researched heavily in drug delivery, 36 besides other applications. 37 However, its application in catalysis is still at an infant stage. 38 While the exact basic monomeric unit structure of sporopollenin is still under investigation and debatable, many studies have suggested that it is composed of aliphatic-polyketide-derived polyvinyl alcohol units and 7-O-p-coumaroylated C16 aliphatic units, crosslinked through a distinctive dioxane moiety featuring functional groups such as hydroxyl, epoxide, and acetal, etc.…”

Ultrasound‐Responsive Oxygen‐Carrying Pollen for Enhancing Chemo‐Sonodynamic Therapy of Breast Cancer

“…Natural pollens have been employed in many biomedical applications. [11,12] According to the various morphologies of pollens from different species, their potential application value has been constantly explored. Take the pollens of sunflowers for instance, the complex three-dimensional (3D) structure with spikes and nanopores on their surface makes them potential carriers for a variety of molecular drugs.…”

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

“…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. 25 − 27 …”