Protein cage

Traditional methods for fabricating nano-scaled arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of self-organizing templates. Due to their intrinsic ability to adopt complex and flexible conformations, proteins have been used to control the size and shape, and also to form ordered two-dimensional arrays of nanopartides. The following examples focus on the use of helical protein templates, such as gelatin and collagen, and protein cages such as ferritin-based molecules. 

Meldrum, F.C., Wade, V.J., Nimmo, D. L., Heywood, B.R. and Mann, S. (1991) Synthesis of inorganic nanophase materials in supramolecular protein cages. Nature, 349, 684-687. 

Douglas, T. and Young, M. (1998) Host-guest encapsulation of materials by assembled virus protein cages. Nature, 393, 152-155. 

Kao, C.C. and Dragnea, B. (2006) Nanopartide-templated assembly of viral protein cages. Nano Letters, 6, 611-615. 

There is no general consensus on why the difference in the quantum yield of photosubstitutions is so large for 02-adducts (4> 10 3) and CO-adducts and on which excited states are responsible for this difference. An explanation based on a different efficiency of the recoordination of released 02 or CO molecules (geminate recombination) can be ruled out, as in the systems with the same biocomplex (e.g. Hb02 and HbCO) both molecules (02 and CO) have nearly identical escaping probability from the protein cage due to their similar size, mass and polarity. The reason could, therefore, lie in the different photoreactive excited states involved. 

Such a unified correlation strongly indicates that the reduction of HRP compound I by thioanisoles proceeds via electron transfer rather than direct oxygen transfer. Electron transfer from the sulfide to HRP compound I in the protein cage might be followed by two competitive processes (i) oxygen rebound to afford the sulfoxide and (ii) diffusion of a sulfenium radical from the protein cage to enable the observation of HRP compound II as shown in Scheme 6 [108]. 

T. Douglas, M Young Host-Guest Encapsulation of Materials by Assembled Vims Protein Cages Nature 393, 152 (1998). 

Engineering Control Over Protein Function Using Chemistry 3.2.3.2 Single Residue Protein Caging... 

Non-covalent insertion of several modified metal cofactors and synthetic metal complexes into protein cavities such as serum albumin (SA) and Mb has been reported [5, 24, 28, 30, 69], If synthetic metal complexes, whose structures are very different from native cofactors, can be introduced into protein cages, the bioconjugation of metal complexes will be applicable to many proteins and metal complexes. Mn(corrole) and Cn(phthalocyanine) are inserted into SA by non-covalent interactions and the composites catalyze asymmetric sulfoxidation and Diels-Alder reactions with up to 74 and 98% ee, respectively (Fig. 2c) [28, 30], Since the heme is coordinated to Tyrl61 in the albumin cavity, determined by X-ray crystal structure [20], it is expected that both Mn(corrole) and Cu(phtalocyanine) are also bound to albumin with the same coordination. The incorporation of synthetic metal complexes in protein cavities using these methods is a powerful approach for asymmetric catalytic reactions. However, there are still some difficulties in further design of the composites for improving reactivities and understanding reaction mechanisms because detailed structural analyses are not available for most of the composites. 

To understand the molecnlar mechanism of biomineralization, it is very important to study the initial metal binding process as well as the process of metal clnster formation. However, little is known so far on the interactions between amino acids and metal clusters. Ferritin and other ferritin-like spherical proteins are known to catalyze biomineralization in the protein cages [4,49]. For example, Fe" ions incorporated in these protein cages are oxidized to Fe " at the ferroxidase center and deposited in the protein large cavities as iron oxides [49]. 

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