The effect of sugar stereochemistry on protein self-assembly: the case of β-casein micellization in different aldohexose solutions

Abstract

Protein self-assembly applications, such as nanoencapsulation of drugs and nutraceuticals, require deep understanding of the parameters governing the micellization process, including the effects of ionic and non-ionic co-solutes, like salts and sugars respectively, which is often overlooked. Herein, with the aim of shedding light on the effect of nonionic cosolute stereochemistry on protein self-assembly, we studied the ternary system of water-protein-sugar by examining the concentration-dependent effects of three aldohexoses, d-glucose (Glu), d-galactose (Gal) and d-mannose (Man) and that of urea, on the micellization of beta casein (β-Cas), using pyrene as a fluorescent probe for the formation of hydrophobic domains. Pyrene's excitation spectra were recorded for several sets of samples with rising protein concentration (0-5 mg ml(-1)), each set with a different co-solute type and concentration. Critical micellization concentration (CMC) and cooperativity of micellization were evaluated according to changes in pyrene spectra as it partitioned from the aqueous environment to the hydrophobic cores of β-Cas micelles. All sugars examined lowered the CMC of β-Cas with increasing sugar concentration and with a diminishing degree of effectiveness (Glu > Gal > Man) which correlated well with the sugars' dynamic hydration number, defined by Uedaira, and correlated negatively with their hydrophobic to hydrophilic molecular surface ratio. These results support the hypothesis that sugars affect protein self-assembly through both changes in water structure and by hydrophobic interactions, both of which are evidenced to be highly sensitive to sugar stereochemistry.

Stimuli-Free Transcuticular Delivery of Zn Microelement Using Biopolymeric Nanovehicles: Experimental, Theoretical, and In Planta Studies

“…Any change in the surrounding polarity, such as when pyrene is encapsulated from an aqueous environment by a hydrophobic-cored aggregate, is expressed by this ratio’s value. 53 Pyrene’s highly hydrophobic nature and low water solubility (2–3 μM) ensure its preference to be present in hydrophobic over hydrophilic environment. These characteristics make pyrene an ideal fluorescent probe for analyzing a substance’s critical aggregate concentration.…”

“…, I 3 ≈ 383 nm and I 1 ≈ 373 nm) in pyrene’s spectrum was used as a quantitative measurement for its microenvironment’s polarity. Any change in the surrounding polarity, such as when pyrene is encapsulated from an aqueous environment by a hydrophobic-cored aggregate, is expressed by this ratio’s value . Pyrene’s highly hydrophobic nature and low water solubility (2–3 μM) ensure its preference to be present in hydrophobic over hydrophilic environment.…”

“…All samples were made in triplicate. CAC values were calculated as the intersection between two linear lines depicting aggregate formation dependent on concentration in solution …”

“…CAC values were calculated as the intersection between two linear lines depicting aggregate formation dependent on concentration in solution. 53 CDs Fluorescence Measurements. CDs fluorescence spectra of CS-CDs (4 mg/mL) samples were measured in a standard 1 cm quartz cell using a computer-controlled Shimadzu, RF-5301PC spectrofluorometer equipped with a 150 W xenon lamp (Ushio Inc., Japan).…”

Method for enhancing bioavailability of myricetin based on self‐assembly of casein–myricetin nanomicelles

“…This self‐assembly process mainly relies on van der Waals forces, hydrogen bonds, electrostatic forces, and coordination bonds, forming ordered, stable and intact analytical structure of self‐assembly system [17]. The materials used for molecules self‐assembly are mostly amphiphilic materials, of which the protein is the most studied [18, 19].…”