Laser Light Scattering Applications in Biotechnology

Alcalase Enzymolysis of Red Bean (adzuki) Ferritin Achieves Nanoencapsulation of Food Nutrients in a Mild Condition

Classical methods to fabricate ferritin-nutrients shell-core nanoparticles usually apply extremely acid/alkaline pH transition, which may cause the activity loss of nutrients or the formation of insoluble aggregates. In this work, we prepared an extension peptide (EP) deleted red bean (adzuki) ferritin (apoRBFΔEP) by Alcalase 3.0T enzymolysis. Such enzymolysis could delete the EP domain and remain the typical shell-like structure of the ferritin. Meanwhile, the α-helix content of apoRBFΔEP was decreased by 5.5%, and the transition temperature (T_m) was decreased by 4.1 °C. Interestingly, the apoRBFΔEP can be disassembled into subunits under a benign condition at pH 4.0 and is assembled to form an intact cage protein when the pH was increased to 6.7. By using this novel route, the epigallocatechin gallate (EGCG) molecules were successfully encapsulated into the apoRBFΔEP cage with an encapsulation ratio of 11.6% (w/w), which was comparable with that by the traditional pH 2.0 transition. The newly prepared EGCG-loaded apoRBFΔEP exhibited a similarly protective effect on the EGCG upon simulated gastrointestinal tract and thermal treatment as compared with the control. In addition, the EGCG-loaded apoRBFΔEP could significantly relieve the ferritin association induced by pH transition, which was superior to traditional method. The thinking of this work will be especially suitable for encapsulating pH-sensitive molecules based on ferritin in a benign condition.

Urea-Driven Epigallocatechin Gallate (EGCG) Permeation into the Ferritin Cage, an Innovative Method for Fabrication of Protein-Polyphenol Co-assemblies

The 8 nm diameter cavity endows the ferritin cage with a natural space to encapsulate food components. In this work, urea was explored as a novel medium to facilitate the formation of ferritin-polyphenol co-assemblies. Results indicated that urea (20 mM) could expand the 4-fold channel size of apo-red bean ferritin (apoRBF) with an increased initial iron release rate υ₀ (0.22 ± 0.02 μM min^-1) and decreased α-helix content (5.6%). Moreover, urea (20 mM) could facilitate the permeation of EGCG into the apoRBF without destroying the ferritin structure and thus form ferritin-EGCG co-assemblies (FECs) with an encapsulation ratio and loading capacity of 17.6 and 2.1% (w/w), respectively. TEM exhibited that FECs maintained a spherical morphology with a 12 nm diameter in size. Fluorescence analysis showed that urea intervention could improve the binding constant K [(1.22 ± 0.8) × 10⁴ M^-1] of EGCG to apoRBF. Furthermore, the EGCG thermal stability was significantly improved (20-60 °C) compared with free EGCG. Additionally, this urea-involved method was applicable for chlorogenic acid and anthocyanin encapsulation by the apoRBF cage. Thus, urea shows potential as a novel potential medium to encapsulate and stabilize bioactive polyphenols for food usage based on the ferritin protein cage structure.

Role of H-1 and H-2 subunits of soybean seed ferritin in oxidative deposition of iron in protein

Naturally occurring phytoferritin is a heteropolymer consisting of two different H-type subunits, H-1 and H-2. Prior to this study, however, the function of the two subunits in oxidative deposition of iron in ferritin was unknown. The data show that, upon aerobic addition of 48-200 Fe(2+)/shell to apoferritin, iron oxidation occurs only at the diiron ferroxidase center of recombinant H1 (rH-1). In addition to the diiron ferroxidase mechanism, such oxidation is catalyzed by the extension peptide (a specific domain found in phytoferritin) of rH-2, because the H-1 subunit is able to remove Fe(3+) from the center to the inner cavity better than the H-2 subunit. These findings support the idea that the H-1 and H-2 subunits play different roles in iron mineralization in protein. Interestingly, at medium iron loading (200 irons/shell), wild-type (WT) soybean seed ferritin (SSF) exhibits a stronger activity in catalyzing iron oxidation (1.10 ± 0.13 μm iron/subunit/s) than rH-1 (0.59 ± 0.07 μm iron/subunit/s) and rH-2 (0.48 ± 0.04 μm iron/subunit/s), demonstrating that a synergistic interaction exists between the H-1 and H-2 subunits in SSF during iron mineralization. Such synergistic interaction becomes considerably stronger at high iron loading (400 irons/shell) as indicated by the observation that the iron oxidation activity of WT SSF is ∼10 times larger than those of rH-1 and rH-2. This helps elucidate the widespread occurrence of heteropolymeric ferritins in plants.