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(From Left) Dr. Angel Lai Yau-tsz, Professor Sun Hongzhe, and Miss Candice Chang Yuen-yan, of the Department of Chemistry

Professor Sun Hongzhe

One such tag, termed a hexahistidine-tag (His-tag), has been used for many years because it is simple and has minimal effect on perturbing the natural functioning of a protein of interest. Large libraries with tens of thousands of proteins each individually encoded with this small tag have thus been developed in recent years. The next question becomes – can we observe where each of these proteins is within the cell and how this changes with time as the cell performs different functions? 

The fluorescent probe can rapidly cross the cell membrane in minutes and emit blue fluorescence only after labeling the target protein in cells. Hence, any actions that cause the movement of proteins in cell can be closely monitored. 

To answer this question, Professor Sun’s research team has developed a novel fluorescent probe to rapidly label
intracellular tagged proteins (in min) with a reduction to only one-fourth of the cost of current methods. Scientists have spent tremendous efforts to monitor this class of proteins in living systems but Professor Sun’s team is the first to have succeeded. Challenges include getting the probe across the cell membrane, ensuring the probe does not disturb the natural functions of the target proteins, and is not toxic to cells. After three-year of efforts, Professor Sun’s team has created, up till now, the only small molecule-based fluorescent probe that can achieve this aim and will help us understand the functions of tens of thousands of proteins in all types of cells, from bacterial cell to mammalian cells and even to highly complex plant tissues. Furthermore, researchers in the group have also developed probes with different colors to enable the observation of the precise localization of multiple proteins within the same cells simultaneously, which is critical to understand how proteins interact with one another. These probes can be readily applied to visualize the actions of drugs on their targets in cells in facilitating drug screening for future drug discovery. Such biotechnology will have a significant impact on our understanding of the proteome – the next frontier after the genome.

Professor Sun Hongzhe
Professor Sun Hongzhe is a professor of the Department of Chemistry at the University of Hong Kong. His research focuses on the biological inorganic chemistry and inorganic chemical biology, especially in metallomics and metalloproteomics. Professor Sun has published a series of work in understanding the functions of metalloproteins and the mechanisms of actions of bismuth-based metallodrugs. He is also a recipient of the Crouch Senior Research Fellow and the Convenor of the e-SRT on Integrative Biology.

Professor Sun was recipient of the HKU Outstanding Research Student Supervisor Award in 2013, awarded in recognition of his excellence in teaching and research.

More information about Professor Sun Hongzhe and his research group can be found from their group’s webpage: http://www.chemistry.hku.hk/staff/hzsun/website2013/Labpage/Home.html

Paper
“Rapid Labeling of Intracellular His-tagged Proteins in Living Cells”
at Proceedings of the National Academy of Sciences of the United States of America
http://www.pnas.org/content/early/2015/02/18/1419598112.abstract

Proceedings of the National Academy of Sciences of the United States of America, referred to as PNAS, is an official journal of the National Academy of Science, USA. PNAS is one of the world’s most-cited multidisciplinary scientific journals, covering publications in biological, physical and social sciences. PNAS is now celebrating the 100th anniversary of establishment.

Chemical Labeling of Proteins for Fluorescence Imaging and His-tagged Protein Library
Chemical labeling of proteins is a technique to investigate the localization, functions and dynamic activity of target proteins in order to understand the biological events in living cells. Scientists have spent tremendous efforts to manipulate fluorescent labeling in studying cellular events. Although genetically-encoded tags (e.g. fluorescent protein-tag) can be readily expressed with target proteins inside cells, they possess potential in deleterious perturbation of protein functions due to their large size. Alternatively, small tag-based fluorescent imaging, utilizing synthetic fluorescent probe to site-specifically interact with short peptide-fused target proteins provides a solution. Successful small molecule-based fluorescent probes include biarsenical FlAsH and its derivatives which bind to the tetracysteine motif of intracellular proteins, and Ni2+-NTA-based probes which interact with the hexahistidine-tag (His-tag) on proteins.

His-tag labeling system has been widely applied in protein purification and elucidation of protein characterization for biological and biotechnological research owing to its advantage in monitoring cellular activities with minimal disturbance to the functions of target proteins. However, due to the constraints of poor membrane permeability of Ni2+-NTA-based fluorescent probes, tracking the large library of His-tagged proteins in living cells is still impossible.

It is, therefore, of great interest to construct membrane-permeable small fluorescent probes in real-time monitoring intracellular His-tagged proteins for the investigation of various cellular events in situ.

For press enquiry, please contact Ms Cindy Chan, Senior Communication Manager of Faculty of Science, at 3917-5286/ 6703- 0212 or by email at cindycst@hku.hk.

Professor Sun Hongzhe’s research team and his collaborators at HKU (from left): Dr. Julian A. Tanner (Dept of Biochemistry), Prof. Chye Mee-Len (Wilson and Amelia Wong Professor in Plant Biotechnology, School of Biological Sciences), Prof. Sun Hongzhe and his research group members from the Department of Chemistry: Dr. Li Hongyan, Miss Yang Ya, Dr. Lai Yau-tsz, Miss Chang Yuen-yan, Miss Chao Ailun 

(From Left) Dr. Lai Yau-tsz and Miss Chang Yuen-yan, of HKU Department of Chemistry