Tunable composites prepared from graphene oxide and zeolitic imidazolate framework-8 for improved selective isolation of hemoglobin

Cu(II)-Loaded Polydopamine-Coated Urchin-like Titanate Microspheres as a High-Performance IMAC Adsorbent for Hemoglobin Separation

Immobilized metal ion affinity chromatography (IMAC) adsorbents generally have excellent affinity for histidine-rich proteins. However, the leaching of metal ions from the adsorbent usually affects its adsorption performance, which greatly affects the reusable performance of the adsorbent, resulting in many limitations in practical applications. Herein, a novel IMAC adsorbent, i.e., Cu(II)-loaded polydopamine-coated urchin-like titanate microspheres (Cu-PDA-UTMS), was prepared via metal coordination to make Cu ions uniformly decorate polydopamine-coated titanate microspheres. The as-synthesized microspheres exhibit an urchin-like structure, providing more binding sites for hemoglobin. Cu-PDA-UTMS exhibit favorable selectivity for hemoglobin adsorption and have a desirable adsorption capacity towards hemoglobin up to 2704.6 mg g-1. Using 0.1% CTAB as eluent, the adsorbed hemoglobin was easily eluted with a recovery rate of 86.8%. In addition, Cu-PDA-UTMS shows good reusability up to six cycles. In the end, the adsorption properties by Cu-PDA-UTMS towards hemoglobin from human blood samples were analyzed by SDS-PAGE. The results showed that Cu-PDA-UTMS are a high-performance IMAC adsorbent for hemoglobin separation, which provides a new method for the effective separation and purification of hemoglobin from complex biological samples.

Metal Organic Framework Nanomaterial-Based Extraction and Proteome Analysis of Membrane and Membrane-Associated Proteins

Membrane proteins (MPs) play a key role in various biological processes, while difficulties still exist in the extraction because of their inherent low abundance and poor solubility caused by high hydrophobicity. Metal organic framework (MOF) materials with good hydrophobic properties have the ability to absorb MPs, especially zeolitic imidazolate framework (ZIF) materials. Here, two MOF materials (ZIF-8 and ZIF-67) were compared for MP extraction, and our results revealed that higher yield was obtained with ZIF-67. After method development, the optimal enrichment effect was obtained when the mass ratio of proteins and ZIF-67 reached 1:20 with 100 mM NaCl in 20% ethanol at 4 °C and pH 9.0. When compared with a commercial kit, the extraction yield increased by 88.11% and the average number of identified MPs elevated by 29.17% with the developed ZIF method. Normal lung cell MRC5 was employed to verify the effectiveness of the ZIF method. Results showed 45.13% increase in yield and 22.88% increase in average number of identified MPs by the ZIF method. Our method was further applied to the enrichment of MPs for high-metastatic (95D) and low-metastatic (95C) human lung cancer cells. A total of 1732 (95D) and 1711 (95C) MPs were identified, among which 710 MPs were dysregulated significantly; 441 upregulated MPs in 95D cells were found to be closely related to the growth, proliferation, and migration of lung cancer cells. Our results collectively demonstrated that ZIF-67 was an ideal material for MP extraction, which might be helpful for analysis of cancer proteomics and discovery of cancer migration associated MPs.

Metal affinity-carboxymethyl cellulose functionalized magnetic graphene composite for highly selective isolation of histidine-rich proteins

A metal affinity-carboxymethyl cellulose functionalized magnetic graphene, namely MGCI-Cu composite, was prepared by successive modifications of graphene oxide nanosheets with magnetic nanoparticles, carboxymethyl cellulose (CMC), iminodiacetic acid (IDA) and then chelated with copper ions. The successful modifications of the graphene surface were demonstrated by various characterizations, and a high density of 6.17 μmol m^-2 for metal affinity groups was obtained. The composite exhibited high adsorption selectivity toward histidine-rich proteins. The adsorption was governed by strong metal affinity binding force between hisitidine residues of proteins and immobilized Cu²⁺ ions of MGCI-Cu composite. In particular, highly selective isolation of hemoglobin (Hb) was achieved in 0.2 mol L^-1 phosphate buffer at pH 8. The adsorption capacity of Hb significantly increased to 769 mg g^-1 in comparison to that of 435 mg g^-1 on metal affinity modified magnetic graphene composite (MGI-Cu) without CMC modification. The adsorbed Hb molecules were recovered with a carbonate buffer (0.2 mol L^-1 pH 10) containing 0.5 mol L^-1 imidazole. MGCI-Cu composite displayed favorable reusability for at least four times after regeneration of the composite by edetic acid (EDTA) and Cu²⁺ solution. The practical applications demonstrated that MGCI-Cu composite could highly selectively isolate Hb from human whole blood and polyhistidine-tagged recombinant protein from Escherichia coli (E. coli) lysate.