Professional Education

  • Master of Science, Peking University (2010)
  • Doctor of Philosophy, University of Illinois at Urbana Champaign (2016)
  • Bachelor of Science, Nanjing University (2005)

Stanford Advisors

All Publications

  • Reversible S-nitrosylation in an engineered azurin NATURE CHEMISTRY Tian, S., Liu, J., Cowley, R. E., Hosseinzadeh, P., Marshall, N. M., Yu, Y., Robinson, H., Nilges, M. J., Blackburn, N. J., Solomon, E. I., Lu, Y. 2016; 8 (7): 670-677


    S-Nitrosothiols are known as reagents for NO storage and transportation and as regulators in many physiological processes. Although the S-nitrosylation catalysed by haem proteins is well known, no direct evidence of S-nitrosylation in copper proteins has been reported. Here, we report reversible insertion of NO into a copper-thiolate bond in an engineered copper centre in Pseudomonas aeruginosa azurin by rational design of the primary coordination sphere and tuning its reduction potential by deleting a hydrogen bond in the secondary coordination sphere. The results not only provide the first direct evidence of S-nitrosylation of Cu(II)-bound cysteine in metalloproteins, but also shed light on the reaction mechanism and structural features responsible for stabilizing the elusive Cu(I)-S(Cys)NO species. The fast, efficient and reversible S-nitrosylation reaction is used to demonstrate its ability to prevent NO inhibition of cytochrome bo3 oxidase activity by competing for NO binding with the native enzyme under physiologically relevant conditions.

    View details for DOI 10.1038/nchem.2489

    View details for PubMedID 27325093

  • A Purple Cupredoxin from Nitrosopumilus maritimus Containing a Mononuclear Type 1 Copper Center with an Open Binding Site. Journal of the American Chemical Society Hosseinzadeh, P., Tian, S., Marshall, N. M., Hemp, J., Mullen, T., Nilges, M. J., Gao, Y. G., Robinson, H., Stahl, D. A., Gennis, R. B., Lu, Y. 2016; 138 (20): 6324–27


    Mononuclear cupredoxin proteins usually contain a coordinately saturated type 1 copper (T1Cu) center and function exclusively as electron carriers. Here we report a cupredoxin isolated from the nitrifying archaeon Nitrosopumilus maritimus SCM1, called Nmar1307, that contains a T1Cu center with an open binding site containing water. It displays a deep purple color due to strong absorptions around 413 nm (1880 M(-1) cm(-1)) and 558 nm (2290 M(-1) cm(-1)) in the UV-vis electronic spectrum. EPR studies suggest the protein contains two Cu(II) species of nearly equal population, one nearly axial, with hyperfine constant A∥ = 98 × 10(-4) cm(-1), and another more rhombic, with a smaller A∥ value of 69 × 10(-4) cm(-1). The X-ray crystal structure at 1.6 Å resolution confirms that it contains a Cu atom coordinated by two His and one Cys in a trigonal plane, with an axial H2O at 2.25 Å. Both UV-vis absorption and EPR spectroscopic studies suggest that the Nmar1307 can oxidize NO to nitrite, an activity that is attributable to the high reduction potential (354 mV vs SHE) of the copper site. These results suggest that mononuclear cupredoxins can have a wide range of structural features, including an open binding site containing water, making this class of proteins even more versatile.

    View details for DOI 10.1021/jacs.5b13128

    View details for PubMedID 27120678

  • Photocaged DNAzymes as a General Method for Sensing Metal Ions in Living Cells ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Hwang, K., Wu, P., Kim, T., Lei, L., Tian, S., Wang, Y., Lu, Y. 2014; 53 (50): 13798-13802


    DNAzymes, which are sequences of DNA with catalytic activity, have been demonstrated as a potential platform for sensing a wide range of metal ions. Despite their significant promise, cellular sensing using DNAzymes has however been difficult, mainly because of the "always-on" mode of first-generation DNAzyme sensors. To overcome this limitation, a photoactivatable (or photocaged) DNAzyme was designed and synthesized, and its application in sensing Zn(II) in living cells was demonstrated. In this design, the adenosine ribonucleotide at the scissile position of the 8-17 DNAzyme was replaced by 2'-O-nitrobenzyl adenosine, rendering the DNAzyme inactive and thus allowing its delivery into cells intact, protected from nonspecific degradation within cells. Irradiation at 365 nm restored DNAzyme activity, thus allowing the temporal control over the sensing activity of the DNAzyme for metal ions. The same strategy was also applied to the GR-5 DNAzyme for the detection of Pb(II), thus demonstrating the possible scope of the method.

    View details for DOI 10.1002/anie.201408333

    View details for Web of Science ID 000345833100027

    View details for PubMedID 25314680

  • Redesigning the blue copper azurin into a redox-active mononuclear nonheme iron protein: preparation and study of Fe(II)-M121E azurin. Journal of the American Chemical Society Liu, J., Meier, K. K., Tian, S., Zhang, J., Guo, H., Schulz, C. E., Robinson, H., Nilges, M. J., Münck, E., Lu, Y. 2014; 136 (35): 12337-12344


    Much progress has been made in designing heme and dinuclear nonheme iron enzymes. In contrast, engineering mononuclear nonheme iron enzymes is lagging, even though these enzymes belong to a large class that catalyzes quite diverse reactions. Herein we report spectroscopic and X-ray crystallographic studies of Fe(II)-M121E azurin (Az), by replacing the axial Met121 and Cu(II) in wild-type azurin (wtAz) with Glu and Fe(II), respectively. In contrast to the redox inactive Fe(II)-wtAz, the Fe(II)-M121EAz mutant can be readily oxidized by Na2IrCl6, and interestingly, the protein exhibits superoxide scavenging activity. Mössbauer and EPR spectroscopies, along with X-ray structural comparisons, revealed similarities and differences between Fe(II)-M121EAz, Fe(II)-wtAz, and superoxide reductase (SOR) and allowed design of the second generation mutant, Fe(II)-M121EM44KAz, that exhibits increased superoxide scavenging activity by 2 orders of magnitude. This finding demonstrates the importance of noncovalent secondary coordination sphere interactions in fine-tuning enzymatic activity.

    View details for DOI 10.1021/ja505410u

    View details for PubMedID 25082811

  • Metalloproteins Containing Cytochrome, Iron-Sulfur, or Copper Redox Centers CHEMICAL REVIEWS Liu, J., Chakraborty, S., Hosseinzadeh, P., Yu, Y., Tian, S., Petrik, I., Bhagi, A., Lu, Y. 2014; 114 (8): 4366-4469

    View details for DOI 10.1021/cr400479b

    View details for Web of Science ID 000335086300011

    View details for PubMedID 24758379

  • Copper-sulfenate complex from oxidation of a cavity mutant of Pseudomonas aeruginosa azurin PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Sieracki, N. A., Tian, S., Hadt, R. G., Zhang, J., Woertink, J. S., Nilges, M. J., Sun, F., Solomon, E. I., Lu, Y. 2014; 111 (3): 924-929


    Metal-sulfenate centers are known to play important roles in biology and yet only limited examples are known due to their instability and high reactivity. Herein we report a copper-sulfenate complex characterized in a protein environment, formed at the active site of a cavity mutant of an electron transfer protein, type 1 blue copper azurin. Reaction of hydrogen peroxide with Cu(I)-M121G azurin resulted in a species with strong visible absorptions at 350 and 452 nm and a relatively low electron paramagnetic resonance gz value of 2.169 in comparison with other normal type 2 copper centers. The presence of a side-on copper-sulfenate species is supported by resonance Raman spectroscopy, electrospray mass spectrometry using isotopically enriched hydrogen peroxide, and density functional theory calculations correlated to the experimental data. In contrast, the reaction with Cu(II)-M121G or Zn(II)-M121G azurin under the same conditions did not result in Cys oxidation or copper-sulfenate formation. Structural and computational studies strongly suggest that the secondary coordination sphere noncovalent interactions are critical in stabilizing this highly reactive species, which can further react with oxygen to form a sulfinate and then a sulfonate species, as demonstrated by mass spectrometry. Engineering the electron transfer protein azurin into an active copper enzyme that forms a copper-sulfenate center and demonstrating the importance of noncovalent secondary sphere interactions in stabilizing it constitute important contributions toward the understanding of metal-sulfenate species in biological systems.

    View details for DOI 10.1073/pnas.1316483111

    View details for Web of Science ID 000329928400027

    View details for PubMedID 24390543

    View details for PubMedCentralID PMC3903256

  • Electrocatalytic and photocatalytic hydrogen production in aqueous solution by a molecular cobalt complex. Angewandte Chemie (International ed. in English) Singh, W. M., Baine, T., Kudo, S., Tian, S., Ma, X. A., Zhou, H., DeYonker, N. J., Pham, T. C., Bollinger, J. C., Baker, D. L., Yan, B., Webster, C. E., Zhao, X. 2012; 51 (24): 5941-5944

    View details for DOI 10.1002/anie.201200082

    View details for PubMedID 22539227

  • Roles of glutamates and metal ions in a rationally designed nitric oxide reductase based on myoglobin PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA Lin, Y., Yeung, N., Gao, Y., Miner, K. D., Tian, S., Robinson, H., Lu, Y. 2010; 107 (19): 8581-8586


    A structural and functional model of bacterial nitric oxide reductase (NOR) has been designed by introducing two glutamates (Glu) and three histidines (His) in sperm whale myoglobin. X-ray structural data indicate that the three His and one Glu (V68E) residues bind iron, mimicking the putative Fe(B) site in NOR, while the second Glu (I107E) interacts with a water molecule and forms a hydrogen bonding network in the designed protein. Unlike the first Glu (V68E), which lowered the heme reduction potential by approximately 110 mV, the second Glu has little effect on the heme potential, suggesting that the negatively charged Glu has a different role in redox tuning. More importantly, introducing the second Glu resulted in a approximately 100% increase in NOR activity, suggesting the importance of a hydrogen bonding network in facilitating proton delivery during NOR reactivity. In addition, EPR and X-ray structural studies indicate that the designed protein binds iron, copper, or zinc in the Fe(B) site, each with different effects on the structures and NOR activities, suggesting that both redox activity and an intermediate five-coordinate heme-NO species are important for high NOR activity. The designed protein offers an excellent model for NOR and demonstrates the power of using designed proteins as a simpler and more well-defined system to address important chemical and biological issues.

    View details for DOI 10.1073/pnas.1000526107

    View details for Web of Science ID 000277591200018

    View details for PubMedID 20421510

  • Lysozyme-stabilized gold fluorescent cluster: Synthesis and application as Hg2+ sensor ANALYST Wei, H., Wang, Z., Yang, L., Tian, S., Hou, C., Lu, Y. 2010; 135 (6): 1406-1410


    Highly fluorescent gold clusters have been synthesized in basic aqueous solution by using lysozyme as reducing and stabilizing agents. The lysozyme-stabilized gold fluorescent clusters (LsGFC) have an average size of 1 nm and emission approximately 657 nm. The fluorescence could be specifically quenched by Hg(2+), so the LsGFC can be used as a sensor for sensitive and selective Hg(2+) detection with a detection limit of 10 nM.

    View details for DOI 10.1039/c0an00046a

    View details for Web of Science ID 000278011800035

    View details for PubMedID 20411205

  • Multiple C-H activations to construct biologically active molecules in a process completely free of organohalogen and organometallic components ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Li, B., Tian, S., Fang, Z., Shi, Z. 2008; 47 (6): 1115-1118

    View details for DOI 10.1002/anie.200704092

    View details for Web of Science ID 000252871400024

    View details for PubMedID 17985336