Browsing by Author "Zhang, Yi"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Applications of Enzymatic Protein Labeling by Protein Farnesyltransferase Towards Dual-Protein Modification and Construction of Targeted Delivery Systems
    (2018-10) Zhang, Yi
    Over the years, protein-based conjugates have been extensively utilized in a variety of areas, including the study of fundamental biology as well as biotechnological and clinical applications. Compared to the non-selective conjugation methods which result in a mixture of modified products, site-specific modification by enzymatic methods provides homogeneously labeled proteins with identical physical properties and functional activities. In the first chapter of this dissertation, I reviewed the recent development (over the last five years) of enzymatic labeling techniques for a panel of ten different enzymes, including sortase A, subtiligase, microbial transglutaminase, protein farnesyltransferase (PFTase), N-myristoyltransferase, phosphopantetheinyl transferase, tubulin tyrosine ligase, lipoic acid ligase, biotin ligase and formylglycine generating enzyme. It is shown that each enzymatic method possesses its advantages and limitations and there is no single solution for all the applications. Therefore, both the protein substrates and the specific applications need to be considered to choose an optimal modification method. Among the ten enzymes being discussed above, PFTase is highly selective with fast kinetics. The enzyme transfers an isoprenoid moiety from farnesyl diphosphate to a C-terminal cysteine of the protein substrate. Consisted of only four amino acid residues, the enzyme recognition sequence is called CaaX-box, where C is the cysteine being modified. To label a protein of interest, a number of isoprenoid analogues bearing bioorthogonal functional groups have been developed, including azides, alkynes, and aldehydes. In this dissertation, I employed two different prenyltransferases to achieve dual- protein labeling and explored the applicability of using PFTase to modify several alternative binding proteins for the construction of targeted delivery systems, including the Designed Ankyrin Repeat Proteins (DARPins), the 10th extracellular domain of human fibronectin III (Fn3) and the nanobodies (VHH). It was found that all three binding proteins could be modified by PFTase successfully with high efficiency. Notably, the labeled DARPins retained the binding ability and specificity. To avoid complicated chromatographic purification process and streamline the production, a capture and release strategy was employed to create DARPin- fluorophore and DARPin-cytotoxin conjugates. Overall, this dissertation explored the utility of enzymatic labeling by PFTase towards various applications.
  • Thumbnail Image
    Item
    Data for Crystal-Chemical Origins of the Ultrahigh Conductivity of Metallic Delafossites
    (2023-11-09) Zhang, Yi; Tutt, Fred; Evans, Guy N; Sharma, Prachi; Haugstad, Greg; Kaiser, Ben; Ramberger, Justin; Bayliff, Samuel; Tao, Yu; Manno, Mike; Garcia-Barriocanal, Javier; Chaturvedi, Vipul; Fernandes, Rafael M; Birol, Turan; Seyfried Jr, William E; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials Lab
    Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 um. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we first report a new approach to PdCoO2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios (>440). Nevertheless, the first detailed mass spectrometry measurements on these materials reveal that they are not ultrapure, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (~1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a previously unconsidered “sublattice purification” mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites. This dataset contains all digital data in the published paper of the same name.
  • Thumbnail Image
    Item
    Exploring Strategies for Promoting Modal Shifts to Transitways
    (Center for Transportation Studies, University of Minnesota, 2015-12) Cao, Jason; Fan, Yingling; Guthrie, Andrew; Zhang, Yi
    Transitways represent large public investments whose positive impacts must be maximized whenever possible to justify the expenditures they entail. Prominent among those looked-for positive impacts is the encouragement of automobile-to-transit mode shifts by attracting increased transitway ridership. This study explores the impacts of travel time, travel cost, and population density on mode choice, using the 2010 Travel Behavior Inventory. We found a monetary value of in-vehicle travel time of $17.5/hour and a transfer penalty of $10, equivalent to 35 minutes in-vehicle travel time. Density, especially at destinations, has important effects, but travel time is the key to promote the shift to transit. The research also employs a Direct Ridership Model (DRM) to predict boardings at the station level as a function of transit-supportive policies. We find that station-area focused policies promoting affordable housing and sidewalks on all streets in station areas or entire cities have a significant and positive impact on ridership if there are sufficient potential destinations in the immediate station area, measured as the number of Google places within 100 meters. Based on our results, we stress the importance of station area affordable housing as a transit system efficiency measure, as well as for the social equity reasons it is usually encouraged. We recommend strengthening proaffordable housing policies and pro-sidewalk policies in Twin Cities station areas, supporting and encouraging for the neighborhood-scale commercial development that is required for their efficacy, and the continued implementation of pro-affordable housing policies and pro-sidewalk policies as the regional transitway system expands.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Public transport use among the urban and rural elderly in China: Effects of personal, attitudinal, household, social-environment and built-environment factors
    (Journal of Transport and Land Use, 2018) Zhang, Yi; Wu, Wei; He, Qian; Li, Chaoyang
    Public transport brings significant benefits to the aging society by providing essential mobility to the elderly. However, few studies have investigated the factors that impact public transport use among the urban or rural elderly. This study explored the effects of personal, attitudinal, household, social environment, and built environment factors on the public transport trips of the elderly. The research data was collected from 274 urban and rural neighborhoods of Zhongshan, a medium-sized Chinese city. The negative binomial regression models suggest that, all else being equal, living in a neighborhood with a high level of public transport service, abundant green space along walking routes connecting home and bus-stops, or a relatively balanced structure of age or income is strongly connected to more public transport trips of the elderly. The results also indicate that a strong preference for public transport is significantly related to the public transport use among the elderly. These findings facilitate our understanding of the correlates of public transport use while providing insights into achieving an effective design of policies to encourage public transport use among the elderly in China.
  • Thumbnail Image
    Item
    Validation Of The Risk Adjustment Method - Adjusted Clinical Groups (ACG) As Applied To The Chinese Healthcare System
    (2015-09) Zhang, Yi
    With the expansion of both health insurance coverage and the scale of health insurance fund, the basic Chinese health insurance has covered 97% of the Chinese population. As a result, the payment from third parties accounts for a large amount of healthcare expense. These result in increasing power from the third party payers to influence the healthcare market and the delivery of care in the long run. Thus, using advanced information technology to improve administrative ability and developing analytical methods for health insurance data to aid managerial decisions and policy implementation are needed. Risk adjustment of health insurance represents an opportunity to improve efficiency and equity of the health system. This study is the first time to validate and evaluate one of the best known risk adjustment methods - the Johns Hopkins Adjusted Clinical Groups (ACG) Case-Mix System to China's health system based on large amounts of Chinese health insurance claims.