The Skaggs Institute
for Chemical Biology
New Amino Acid Building Blocks
P.G. Schultz, E.M. Brustad, J. Grünewald, J. Guo, H.S. Lee, C.C. Liu, F.B. Peters, T.S. Young
Almost all processes
of living cells, from gene regulation and information processing to photosynthesis,
are carried out by proteins. These are large molecules synthesized from 20 amino
acid building blocks. This set of 20 amino acids is the basis for the genetic code,
the code that specifies the relationship between the nucleotide sequence of a gene
and the amino acid sequence of a protein. This fact leads to rather interesting
questions: Why does every form of life have the same set of building blocks? Why
not 21 or more? Moreover, if we can add new amino acid building blocks to the genetic
code, will we be able to create proteins or even cells with enhanced chemical, physical,
or biological properties?
continue to address this issue by using chemical and molecular biological methods
to add new components to the protein biosynthetic machinery of bacteria. Using this
approach, we effectively expanded the genetic code of both prokaryotes and eukaryotes
by genetically encoding new amino acids (including photoaffinity labels, chemically
reactive amino acids, posttranslationally modified amino acids, and amino acids
with altered electronic and steric properties) in response to unique 3- and 4-base
Currently, we are exploring additional
amino acids with novel biological and physicochemical properties, other organisms,
and a number of biomedical applications of this technology. For example, in the
past year, we showed that tolerance against the self-antigen TNF-α
in mice can be broken by the selective introduction of p-nitrophenylalanine.
This research promises to greatly facilitate the generation of cancer vaccines
and vaccines against third-world pathogens; we are currently extending it to lung
and breast cancer vaccines and vaccines against tuberculosis, malaria. and HIV disease.
We also genetically encoded a boronate-containing amino acid for the scarless purification
of proteins, selective protein modification, and the development of selective antibodies
to both glycoproteins and serine proteases involved in viral infections and cancer.
In addition, we genetically encoded a hydroxyquinoline metal ion–binding amino
acid for heavy-atom phasing in protein structure determination and for the introduction
of radioisotopes into antibodies for cancer therapy and imaging.
In other studies, we used a phenylselenide-containing
amino acid to generate proteins containing posttranslationally modified lysine residues
to study the role of histone modification in the epigenetics of cancer and developmental
biology. We also showed that phage display can be used to select anti-gp120 sulfotyrosine-containing
antibodies with enhanced affinities relative to the naturally sulfated anti-gp120
antibody. This result shows for the first time that an expanded genetic code can
confer an evolutionary advantage and may lead to the generation of therapeutic proteins
or peptides with improved biological or pharmacologic properties due to the presence
of unnatural amino acids.
We also genetically encoded the fluorophore
prodan in mammalian cells to facilitate cellular studies of protein structure, function,
and localization; genetically encoded an unnatural amino acid that can cleave the
polypeptide backbone in a light-dependent fashion as a cell biological tool; and
biosynthesized DNA-binding proteins that can oxidatively cleave the DNA backbone
in a sequence-specific fashion as a probe of protein-DNA recognition. Furthermore,
we showed that unnatural amino acids can be used to selectively introduce fluorescence
resonance energy transfer pairs into proteins for single-molecule imaging studies,
and we developed a high-yield Pichia expression system to produce therapeutic
proteins containing unnatural amino acids.
Brustad, E., Bushey, M.L., Brock, A., Chittuluru, J., Schultz, P.G. A promiscuous aminoacyl-tRNA synthetase that incorporates cysteine, methionine, and
alanine homologs into proteins. Bioorg. Med. Chem. Lett. 18:6004, 2008.
Brustad, E., Bushey, M.L., Lee, J.W., Groff, D., Liu, W., Schultz, P.G. A genetically encoded boronate-containing amino acid. Angew. Chem. Int. Ed. 47:8220,
Grünewald, J., Tsao, M.-L., Perera, R., Dong, L., Niessen, F., Wen, B.G., Kubitz, D.M., Smider, V.V., Ruf, W., Nasoff, M., Lerner, R.A., Schultz, P.G.
Immunochemical termination of self-tolerance. Proc. Natl. Acad. Sci. U. S. A. 105:11276, 2008.
Guo, J., Wang, J., Anderson, J.C., Schultz, P.G. Addition of an α-hydroxy acid to the genetic code of bacteria. Angew. Chem. Int. Ed. 47:722, 2008.
Guo, J., Wang, J., Lee, J.-S., Schultz, P.G. Site-specific incorporation of methyl- and acetyl-lysine analogues into recombinant proteins. Angew. Chem. Int.
Ed. 47:6399, 2008.
Lee, J., Hong, J., Nam, T.-G., Peters, E.C., Orth, A.P., Geierstanger, B.H., Goldfinger, L.E., Ginsberg, M.H., Cho, C.Y., Schultz, P.G. A small molecule
inhibitor of α4 integrin-dependent cell migration. Bioorg. Med. Chem., in press.
Lemke, E.A., Summerer, D., Geierstanger, B.H., Brittain, S.M., Schultz, P.G. Control of protein phosphorylation with a genetically encoded photocaged amino acid.
Nat. Chem. Biol. 3:769, 2007.
Tippmann, E.M., Liu, W., Summerer, D., Mack, A.V., Schultz, P.G. A genetically encoded diazirine photocrosslinker in Escherichia coli. ChemBioChem