| Protein is a biological macromolecule widely existing in nature.In recent years,the application of proteins in drug delivery,biocatalysis,biosynthesis,vaccine etc.has aroused great attention with the development of science and technology.Ferritin is a protein that regulates the balance of metabolism in organisms by utilizing the self-assembly properties of proteins.Ferritin has several advantages like high symmetry,stability and solubility,which have important research value in nanomaterials and medical fields.Human-derived heavy chain ferritin,a cage protein with an inner diameter of 8 nm and a wavelength of 12 nm,is consists of 24 ferritin subunits.Each ferritin subunit has A,B,C,D and E five ? helices and BC loop.Several studies have shown that designing and modifying ferritin self-assembling interfaces and subunits can achieve targeted changes in the structure and function of ferritin.By molecular design and transformation of ferritin,this study aims to obtain changes in the self-assembly form and regulation of ferritin,and expand its applications in drug delivery,protein framework materials,etc.The obtained research results are descried as following:1.There is a hydrophobic core at each end of the parallel 4-helix cluster of ferritin subunits.Hydrophobic forces play a vital role in maintaining the spatial structure of ferritin subunits.By removing some of the key amino acids to exposed the hydrophobic core to the solution,these two subunits transformed into a new self-assembled form under the influence of hydrophobicity.In this work,the amino acids on the D and E helix of ferritin subunits were selectively deleted,and a variety of ferritin mutants were constructed.Finally,it was found that after deleting amino acids 135-183 of the recombinant human heavy chain ferritin subunit,ferritin formed an 8-mer nano-ring structure.By analyzing its crystal structure carefully,it is discovered that the mutant forms a new three-dimensional porous nano-biomaterial.In addition,the molecular mechanism of the 8-mer ring structure was obtained through detailed analysis of the interfacial interactions.This study provides new methods and ideas for designing and forming self-assembling proteins with different structures and functions.2.Ferritin is a potential drug carrier due to its non-toxic,biodegradable,good biocompatibility and tumor cell targeting characteristics.Ferritin can be disaggregated into single subunits at p H ? 2.0.When the p H is adjusted to neutral again,ferritin will renaturate into a cage structure,and embed small molecule drugs in the ferritin cavity.However,this method suffers from low renaturation rate and destruction of drug molecular structure.It is necessary to design and modify ferritin to embed and transport drug molecules under mild conditions.In this work,based on a careful study of human heavy chain ferritin subunit interactions,we design and modify the loop area between the spirals A and B(AB loop).As a result,ferritin can drug entrapment at p H = 4.0,and the protein refolding efficiency is as high as 90%.The obtained crystal structure proves that the modification of the AB loop has significantly reduced the interaction between ferritin cage subunits.At the same time,the design of the AB loop does not affect the cage structure and tumor targeting of ferritin.This research has laid a solid foundation for further expanding the application of ferritin in drug delivery. |
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