Miljan Simonovic

    Email Address:
    College: Medicine Department: Biochemistry and Molecular Genetics
    Title: Assistant Professor
    Office: MBRB 1354 Phone: 312.996.0059
    Participating in the Chancellor’s Undergraduate Research Awards program: Yes

    Research Interest:
    Our laboratory primarily studies mechanisms that ensure fidelity of mRNA translation. Misinsertion of amino acids into the growing polypeptide chain may cause protein misfolding or may yield proteins with different properties. These processes often cause the development of pathologic conditions in humans.

    First, we are studying the mechanism of synthesis of the 21st amino acid - selenocysteine. Although found in only 25 human proteins, selenocysteine is essential for survival. Erroneous replacement of selenocysteine with serine or cysteine renders selenoenzymes inactive, thus, affecting critical cellular processes such as the removal of reactive oxygen species and thyroid hormone activation. Four human enzymes catalyze selenocysteine synthesis in a process that is dependent on selenocysteine tRNA. All enzymes evolved to bind selenocysteine tRNA with high affinity. This is in a striking contrast to 20 standard amino acids, which are synthesized in their free form. The goal is to explain at the structural level the substrate specificity of the human selenocysteine-synthetic enzymes. The general methodology is outlined in our recent Science paper [Palioura et al., Science (2009)]. Finally, the problem is addressed by using molecular components derived from an archaeal organism. This approach will reveal the level of conservation in the process among the organisms that are evolutionarily quite distant.

    Second, we are studying the mechanism by which essential micronutrient selenium is incorporated into the amino acid selenocysteine. In particular, catalytic mechanisms of the human selenophosphate synthase 2 and selenocysteine synthase are in the focus of the study. The former enzyme promotes the insertion of selenium into selenophosphate, whereas the latter one promotes the selenium transfer from selenophosphate to the amino-acid side chain. The goal is to visualize each step of the catalytic cycle at high resolution.

    Third, we are studying the mechanism by which human elongation factors select their tRNA substrates. While the general elongation factor binds all tRNAs but selenocysteine tRNA, the selenocysteine-specific elongation factor binds only selenocysteine tRNA and rejects all other tRNAs. The elongation factors are one of the last checkpoints that prevent the misinsertion of amino acids. The goal of this project is to reveal a structural basis for the substrate specificity of both elongation factors.

    Minimum time commitment in hours per week: 6-10

    Qualifications of a Student:
    The student should have a strong GPA with a major in basic biomedical sciences (chemistry, biochemistry, biology, biophysics, pre-med). The prior laboratory experience is a plus, but not necessary.

    Brief Summary of what is expected from the student:
    A specific project will be assigned to every student. Besides learning the basic molecular biology and biochemistry techniques, the student may be exposed to the advanced methods routinely used in structural biology. The work will involve preparation of the mutant enzymes and tRNA constructs, purification of recombinant proteins, in vitro transcription and tRNA purification, binding assays, protein-tRNA complex purification and protein crystallization.

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