Methanobactin: Metal binding properties, physiological function and biosynthesis

Methanobactins (mbs) are low molecular mass (\u3c 1300 Da) modified peptides secreted by many methanotrophs or methane oxidizing bacteria to sequester copper from the environment. To date, methanobactin has been structurally characterized from six methanotrophs and can be divided into two groups. Group I methanobactins are represented by methanobactins from Methylosinus trichosporium OB3b and Methylosinus sp. LW4. This group is characterized by the presence of two oxazolone rings with adjacent thioamide groups. Two nitrogens from the oxazolone rings and two sulfurs from the thioamide groups come together to form a copper coordination site in distorted tertrahedral geometry. This group of methanobactin also has two cysteines in the mature protein that form a stable disulfide bond. The second group is composed of methanobactins from four different Methylocystis species. This group of methanobactins has a hairpin like structure following copper binding with sulfate group attached to serine or threonine and is structurally more dynamic than group I methanobactins. This group is also characterized by the presence of a C-terminal oxazolone ring with an associated thioamide and either an N-terminal imidazolone or pyrazinedione group and an associated thioamide. The first part of this dissertation is focused on the study of methanobactin binding to various non-copper metals such as mercury and gold and the role of that binding of noncopper metals has on the physiology of methanotrophs. The second part of this dissertation is focused on understanding the post-translational modifications required for methanobactin. Until recently, the biosynthesis was assumed to be via a non-ribosomal peptide synthase or polyketide synthase. However, during the course of my dissertation, we determined that methanobactin is indeed produced ribosomally and post-translationally modified. I show in this dissertation that TonB-dependent transporter gene in the methanobactin gene cluster is involved in the uptake of copper-bound methanobactin. In addition, we demonstrate that mbnN is involved in the deamination of the N-terminal oxazolone ring, a post-translational modification required in the formation of the N-terminal oxazolone ring in the methanobactin from Methylosinus trichosporium OB3b. The results and methods used in this research would further help determine the role of other genes involved in biosynthesis of methanobactin and bioengineer methanobactin for various human and animal health purposes. In light of recent evidence of methanobactin being effective chelator of excess copper in Wilson’s disease in rat models, understanding the biosynthesis of methanobactin has become more important

Potential Distribution of the Critically Endangered Chinese Pangolin (Manis pentadactyla) in Different Land Covers of Nepal: Implications for Conservation

Anthropogenic activities have driven many wildlife species towards extinction. Among these species, the geographic distributions of many are poorly documented, which can limit the effectiveness of conservation. The critically endangered Chinese pangolin (Manis pentadactyla) is experiencing population decline throughout its range due to land-use changes and illegal trade for food and traditional medicine. Using distribution records and maximum entropy modeling, we predicted the potential distribution of the Chinese pangolin across Nepal. Most suitable potential habitats of the Chinese pangolin occurred in forest areas of the mid-hill region in central and eastern Nepal, followed by cultivated land. Almost all potential suitable habitats of the Chinese pangolin occurred outside of protected areas, and most of them were encroached upon by cultivated land, human settlements, and infrastructure developments. The results from this study provide baseline information on the potential suitable habitats of the Chinese pangolin in Nepal, which helps to develop site- and species-specific management plans and to identify priority areas to minimize the current threats to the pangolin and enhance the stewardship of species conservation