Design of
Functional Miniature Metalloproteins
Protein-bound metal ions play essential roles in such fundamental life processes as respiration, photosynthesis, tissue remodeling, and signal transduction. Work being pursued in our group seeks to prepare a new class of synthetic metalloproteins which can mimic, enhance, or even expand the repertoire of chemical functions now being performed by natural metalloenzymes. We are particularly interested in designing “miniature metalloproteins” which possess novel photoactive properties for use in such applications as solar energy conversion, photodynamic tumor therapy, and drug delivery systems.
Protein-bound metal ions play essential roles in such fundamental life processes as respiration, photosynthesis, tissue remodeling, and signal transduction. Work being pursued in our group seeks to prepare a new class of synthetic metalloproteins which can mimic, enhance, or even expand the repertoire of chemical functions now being performed by natural metalloenzymes. We are particularly interested in designing “miniature metalloproteins” which possess novel photoactive properties for use in such applications as solar energy conversion, photodynamic tumor therapy, and drug delivery systems.
Figure 1. Computer generated schematic of the self-assembled Cu(I) metalloprotein which displays a strong room-temperature luminescence at 600 nm.
The design of such
functional metalloproteins presents a formidable challenge
to chemists and our research addresses several fundamental problems in
this
field: 1) the design and synthesis of protein structures capable
of
binding specific transition metal ions, 2) the incorporation of useful
photophysical
and photochemical properties into these systems, and 3) understanding
the
ways that these properties can be modified, and perhaps controlled, by
the
protein environment.
Our approach to these problems begins with the use of solid-phase peptide synthesis to design self-assembling peptide structures which incorporate native-like metal-binding domains into their hydrophobic interiors in a manner similar to that found in naturally occurring metalloproteins (Figure 1). In one such example, a 30-residue polypeptide was prepared whose sequence was designed to be similar to those known to form two-stranded α-helical coiled-coils but modified to contain the native-like Cys-X-X-Cys metal-binding domain. Addition of Cu(I) to this system resulted in the spontaneous self-assembly of a 4-helix bundle which contained a cyclic Cu4Cys4- cofactor, as determined by X-ray absorption spectroscopy. It is of interest to note that this metallopeptide exhibits an intense room temperature luminescence at 600 nm and can be used as a photoinduced electron-transfer reagent capable of reducing a large number of inorganic molecules.
Our approach to these problems begins with the use of solid-phase peptide synthesis to design self-assembling peptide structures which incorporate native-like metal-binding domains into their hydrophobic interiors in a manner similar to that found in naturally occurring metalloproteins (Figure 1). In one such example, a 30-residue polypeptide was prepared whose sequence was designed to be similar to those known to form two-stranded α-helical coiled-coils but modified to contain the native-like Cys-X-X-Cys metal-binding domain. Addition of Cu(I) to this system resulted in the spontaneous self-assembly of a 4-helix bundle which contained a cyclic Cu4Cys4- cofactor, as determined by X-ray absorption spectroscopy. It is of interest to note that this metallopeptide exhibits an intense room temperature luminescence at 600 nm and can be used as a photoinduced electron-transfer reagent capable of reducing a large number of inorganic molecules.
Metal-peptide
Nanoassemblies
The study of supramolecular materials having nanometer-scale dimensions has gained in importance due to the potential of such systems to impact many areas of science and technology. As such, continuing effort is being devoted to create new ways in which discrete molecular subunits can be organized into larger material components, and it is within this context that the study of non-covalent assembly processes has become the focus of special interest. This project seeks to develop a previously unexplored route towards the non-covalent assembly of functional nanostructures by combining the principles of supramolecular coordination chemistry with those of de novo protein design.
The study of supramolecular materials having nanometer-scale dimensions has gained in importance due to the potential of such systems to impact many areas of science and technology. As such, continuing effort is being devoted to create new ways in which discrete molecular subunits can be organized into larger material components, and it is within this context that the study of non-covalent assembly processes has become the focus of special interest. This project seeks to develop a previously unexplored route towards the non-covalent assembly of functional nanostructures by combining the principles of supramolecular coordination chemistry with those of de novo protein design.
Figure 2. Limiting structures of metal-peptide nanoassemblies formed by the coordination of square planar metal complexes to self-assembling peptide structures.
The design of these systems is
based on the construction of the 90° “metal-peptide
corners” formed by binding two 30-mer polypeptides to the cis positions
of
either square planar or octahedral metal complexes. The peptide
sequences
are chosen for their ability to self-assemble into two-stranded
coiled-coils,
but modified to place a metal-binding residues at solvent-exposed
positions.
This design enables the corner units to self-assemble into discrete
nanoassemblies
through the formation of inter-subunit coiled-coils (Figure 1) to
produce
two limiting structural motifs: extended linear chains, and/or closed
peptide
nanoboxes.
Ongoing work will explore the ability of this new class of metallo-peptide nanoassemblies to have applications in biology, medicine, and technology such as the formation of artificial membrane channels, and/or the ability to act as drug delivery systems.
Ongoing work will explore the ability of this new class of metallo-peptide nanoassemblies to have applications in biology, medicine, and technology such as the formation of artificial membrane channels, and/or the ability to act as drug delivery systems.