Browsing by Author "Xiong, Xin"

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Open Access
China’s environmental solutions
(2023) Schmid, Rolf; Xiong, Xin
China emits unproportionately high concentrations of CO2 and, due to rapid population growth and industrialization, suffers from air, water, and soil pollution. However, many of these challenges for sustainable growth are being vigorously addressed, and China aims at a CO2 emission peak by 2030 and carbon neutrality by 2060 (“dual carbon policy”). In addition, nation-wide programs attempt to achieve reforestation and ecological restoration. By 2025, core elements of a “bioeconomy” and a circular economy are expected to be ready. Many of these programs extend into China’s international “belt-and-road” initiative (BRI). In this article, we briefly describe the present achievements of China’s environmental solutions and the country’s visions for a “digital, eco-friendly civilization.
Open Access
New insights into structure and function of type I collagen
(2008) Xiong, Xin; Brunner, Herwig (Prof. Dr. techn.)
Collagen is one of the most abundant proteins in mammalians and strongly conserved throughout evolution. It constitutes one third of the human proteome and comprises three-quarters of the dry weight of human skin. It is widely accepted as a major structural component in animal body such as in bones, cartilage and skins. More and more studies have shown that, in addition to the structural function, collagens can induce or regulate many cellular functions and processes such as cell differentiation, cell motion, cell communication and apoptosis. Furthermore, its unique triple helix structure gained more attention since it is responsible for its high stability and biological function. Due to the high accessibility, Type I and Type III collagen are widely studied and frequently used as biocompatible materials in cell culture, tissue engineering and medical technology. Until now the understanding of the molecular mechanisms for collagen assembly is of great medical and also biotechnological importance. Here, large amounts of highly purified homogeneous Type I collagen have been obtained from rat tail tendon by a simple two-step purification involving extraction with 9 M urea followed by Superose 12 chromatography. This simple two step purification of Type I collagen is up-scalable. The yield is up to 95%. The product could be easily lyophilized and stored. AFM and SEM images showed a structure similar to natural collagen. This collagen was extensively characterized by different biochemical, physical and cell biological methods. Mass spectrometry identified only collagen Type I peptides indicating that the extracted collagen was homogeneous. The comparison between urea-extracted (UC) collagen and acetic acid-extracted collagen (AC) showed significant differences whereby the UC was not degraded or hydrolyzed as in acetic acid. Furthermore, tandem MS analyses showed some interesting post-translational modifications, which will result in new insights into collagen structure in vivo. The purified collagen was renatured quantitatively by dialysis against water to form triple-helices, as judged by UV-circular dichroism. The collagen dissolved in 8M urea exhibits a unique reversible aggregation behavior which is not affected by the presence of reducing agents. UV-circular dichroism analysis shows that collagen initiates triple helix formation at 4 M urea or below. This triple helix structure is comparable to that observed with synthetic collagen peptides. Cultures of a 3T3 mouse embryonic fibroblast cells incubated with urea-extracted collagen showed a higher motility than those grown with acetic acid-extracted collagen as judged by light microscopy and scanning electron microscopy. The real time PCR showed significant difference on transcriptional level and showed clearly up regulation of the genes involved in response to mechanical stress in AC but not in UC and reference culture in medium. All these results indicate a benefit of UC for biotechnological/biomedical applications. The urea-extracted collagen exhibits a unique reversible-aggregational phenomenon during gel filtration in 8 M urea. We could show that covalent bonds and cross-linkings are not involved. This observation and subsequently extensive mass spectrometric analyses led to a new model of triple-helical assembly and a hypothesis about the collagen export, which may offer some new insights into understanding of collagen structure and transport from cytosol to extracellular space. The results presented here have led to an industrial patent (patented on 04. 30th. 2008). A manuscript was submitted to FEBS J for publication.