Trp RNA-Binding Attenuation Protein in Complex with L-Tryptophan
Every cell of living beings has all information as DNA to maintain the life, creating the body, reacting to the environment, etc. Depending on the location where the cell exists in the body, each cell expresses different kinds of proteins at suitable amount. To control which protein should be expressed and how much is necessary, an elaborate system exists. The amount of the proteins should also respond to the environment. When a protein is necessary, the gene which produces the protein is activated, as ON state. When the protein is sufficient, the gene is inactivated, as OFF state. To control the gene ON and OFF, regulatory proteins work. For example, in bacteria, one of the regulatory proteins called “tryptophan repressor protein” with two tryptophan molecules binds to the DNA at specific region called operator to interrupt the production of the enzymes for tryptophan biosynthesis. This means when tryptophan is enough in cells, the expression of the enzymes for tryptophan biosynthesis is halted, whereas when tryptophan is not enough, tryptophan repressor protein without tryptophan molecule does not bind to DNA, allowing the expression of the enzymes for tryptophan biosynthesis. From the view point of the conformational change of tryptophan repressor protein, the binding of two tryptophan molecules increase the distance between the two helices which recognize the DNA (operator), allowing the repressor protein to fit tightly on the operator.
The structure shown here is also tryptophan molecule depending regulatory protein of Bacillus subtilis to control the expression of the enzymes for tryptophan biosynthesis. This regulatory protein works also depending on the mRNA piece which is transcribed preceding the structural genes. So this protein is named “try RNA-binding attenuation protein; TRAP”, meaning this regulatory protein is doubly regulated by tryptophan molecules and mRNA pieces. When tryptophan molecules and mRNA pieces are enough to bind to TRAP, the expression of the enzymes for tryptophan biosynthesis is halted. This structure is a complex of TRAP with tryptophan molecules. It shows a doughnut-like structure with a large central hole, constructed with eleven identical segments, each of which is made by a 7-stranded antiparallel β-sheets. Eleven tryptophan molecules fit in cleft between adjacent segments. The evidence that eleven U/GAG repeats of mRNA bind to this TRAP with eleven tryptophan molecules by biological experiment, make us to imagine the mRNA molecule would bind to the surface of this repressor protein. The structural information about the interaction between activated repressor protein and DNA molecule is also waited.
Protein Data Bank (PDB)
Antson, A.A. Otridge, J. Brzozowski, A.M. Dodson, E.J. Dodson, G.G. Wilson, K.S. Smith, T.M. Yang, M. Kurecki, T. Gollnick, P.; "The structure of trp RNA-binding attenuation protein."; Nature; (1995) 374:693-700 PubMed:7715723.
author: Sachiyo Nomura