All Publications

  • Combinatorial optimization of mRNA structure, stability, and translation for RNA-based therapeutics. Nature communications Leppek, K., Byeon, G. W., Kladwang, W., Wayment-Steele, H. K., Kerr, C. H., Xu, A. F., Kim, D. S., Topkar, V. V., Choe, C., Rothschild, D., Tiu, G. C., Wellington-Oguri, R., Fujii, K., Sharma, E., Watkins, A. M., Nicol, J. J., Romano, J., Tunguz, B., Diaz, F., Cai, H., Guo, P., Wu, J., Meng, F., Shi, S., Participants, E., Dormitzer, P. R., Solorzano, A., Barna, M., Das, R. 2022; 13 (1): 1536


    Therapeutic mRNAs and vaccines are being developed for a broad range of human diseases, including COVID-19. However, their optimization is hindered by mRNA instability and inefficient protein expression. Here, we describe design principles that overcome these barriers. We develop an RNA sequencing-based platform called PERSIST-seq to systematically delineate in-cell mRNA stability, ribosome load, as well as in-solution stability of a library of diverse mRNAs. We find that, surprisingly, in-cell stability is a greater driver of protein output than high ribosome load. We further introduce a method called In-line-seq, applied to thousands of diverse RNAs, that reveals sequence and structure-based rules for mitigating hydrolytic degradation. Our findings show that highly structured "superfolder" mRNAs can be designed to improve both stability and expression with further enhancement through pseudouridine nucleoside modification. Together, our study demonstrates simultaneous improvement of mRNA stability and protein expression and provides a computational-experimental platform for the enhancement of mRNA medicines.

    View details for DOI 10.1038/s41467-022-28776-w

    View details for PubMedID 35318324

  • A p53-dependent translational program directs tissue-selective phenotypes in a model of ribosomopathies. Developmental cell Tiu, G. C., Kerr, C. H., Forester, C. M., Krishnarao, P. S., Rosenblatt, H. D., Raj, N., Lantz, T. C., Zhulyn, O., Bowen, M. E., Shokat, L., Attardi, L. D., Ruggero, D., Barna, M. 2021


    In ribosomopathies, perturbed expression of ribosome components leads to tissue-specific phenotypes. What accounts for such tissue-selective manifestations as a result of mutations in the ribosome, a ubiquitous cellular machine, has remained a mystery. Combining mouse genetics and in vivo ribosome profiling, we observe limb-patterning phenotypes in ribosomal protein (RP) haploinsufficient embryos, and we uncover selective translational changes of transcripts that controlling limb development. Surprisingly, both loss of p53, which is activated by RP haploinsufficiency, and augmented protein synthesis rescue these phenotypes. These findings are explained by the finding that p53 functions as a master regulator of protein synthesis, at least in part, through transcriptional activation of 4E-BP1. 4E-BP1, a key translational regulator, in turn, facilitates selective changes in the translatome downstream of p53, and this thereby explains how RP haploinsufficiency may elicit specificity to gene expression. These results provide an integrative model to help understand how in vivo tissue-specific phenotypes emerge in ribosomopathies.

    View details for DOI 10.1016/j.devcel.2021.06.013

    View details for PubMedID 34242585

  • The Mammalian Ribo-interactome Reveals Ribosome Functional Diversity and Heterogeneity. Cell Simsek, D., Tiu, G. C., Flynn, R. A., Byeon, G. W., Leppek, K., Xu, A. F., Chang, H. Y., Barna, M. 2017; 169 (6): 1051-1065 e18


    During eukaryotic evolution, ribosomes have considerably increased in size, forming a surface-exposed ribosomal RNA (rRNA) shell of unknown function, which may create an interface for yet uncharacterized interacting proteins. To investigate such protein interactions, we establish a ribosome affinity purification method that unexpectedly identifies hundreds of ribosome-associated proteins (RAPs) from categories including metabolism and cell cycle, as well as RNA- and protein-modifying enzymes that functionally diversify mammalian ribosomes. By further characterizing RAPs, we discover the presence of ufmylation, a metazoan-specific post-translational modification (PTM), on ribosomes and define its direct substrates. Moreover, we show that the metabolic enzyme, pyruvate kinase muscle (PKM), interacts with sub-pools of endoplasmic reticulum (ER)-associated ribosomes, exerting a non-canonical function as an RNA-binding protein in the translation of ER-destined mRNAs. Therefore, RAPs interconnect one of life's most ancient molecular machines with diverse cellular processes, providing an additional layer of regulatory potential to protein expression.

    View details for DOI 10.1016/j.cell.2017.05.022

    View details for PubMedID 28575669

  • In Vitro Selection of a DNA-Templated Small-Molecule Library Reveals a Class of Macrocyclic Kinase Inhibitors JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Kleiner, R. E., Dumelin, C. E., Tiu, G. C., Sakurai, K., Liu, D. R. 2010; 132 (33): 11779-11791


    DNA-templated organic synthesis enables the translation of DNA sequences into synthetic small-molecule libraries suitable for in vitro selection. Previously, we described the DNA-templated multistep synthesis of a 13,824-membered small-molecule macrocycle library. Here, we report the discovery of small molecules that modulate the activity of kinase enzymes through the in vitro selection of this DNA-templated small-molecule macrocycle library against 36 biomedically relevant protein targets. DNA encoding selection survivors was amplified by PCR and identified by ultra-high-throughput DNA sequencing. Macrocycles corresponding to DNA sequences enriched upon selection against several protein kinases were synthesized on a multimilligram scale. In vitro assays revealed that these macrocycles inhibit (or activate) the kinases against which they were selected with IC(50) values as low as 680 nM. We characterized in depth a family of macrocycles enriched upon selection against Src kinase, and showed that inhibition was highly dependent on the identity of macrocycle building blocks as well as on backbone conformation. Two macrocycles in this family exhibited unusually strong Src inhibition selectivity even among kinases closely related to Src. One macrocycle was found to activate, rather than inhibit, its target kinase, VEGFR2. Taken together, these results establish the use of DNA-templated synthesis and in vitro selection to discover small molecules that modulate enzyme activities, and also reveal a new scaffold for selective ATP-competitive kinase inhibition.

    View details for DOI 10.1021/ja104903x

    View details for Web of Science ID 000281066400067

    View details for PubMedID 20681606

    View details for PubMedCentralID PMC2924185

  • Theoretical mechanisms and kinetics of the hydrogen abstraction reaction of acetone by chlorine radical CHEMICAL PHYSICS LETTERS Tiu, G. C., Tao, F. 2006; 428 (1-3): 42-48