Westermann, Linda Maria (2021) Novel metal-containing enzymes : missing link in the marine phosphorus cycle? PhD thesis, University of Warwick.

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Abstract

Phosphorus (P) is considered one of the most essential elements for living organisms. Due to its natural reactivity P only exists chemically bonded either as organic or inorganic phosphate (Pi), the preferred source of P for organisms. Ocean surface waters are often Pi limited and depend on exogenic fluxes to fuel marine ecosystems with this much-needed nutrient. Upon entering ocean waters, all sources of P enter the marine P cycle, a huge network that describes the various transformations and removal of P in the marine ecosystem. Oceans regulate the climate and represent an important sink for greenhouse gases. Therefore, climate change is no longer considered a danger for mankind alone, but there is increasing evidence that it will also dramatically impact our most important ecosystem. Because of this, it is necessary to fully understand marine nutrient cycles to allow more precise predictions for the future. My PhD project aimed to develop a better understanding of enzymes that are involved in Pi acquisition from organic P compounds in the marine environment and particularly, to understand how
bacterial and archaeal membrane phospholipid headgroups are used as a source of P. I utilised a proteomic approach to identify key enzymes that are involved in the degradation and transport of these phospholipid headgroups. In addition, protein overexpression, enzyme activity assays, and substrate specificity evaluations were performed to characterise some of these prominent proteins found in the proteomics data. This thesis describes the identification and characterisation of two novel substrate-binding proteins (SBP) in the marine Roseobacter Phaeobacter sp. MED193 (MED193) that are essential for the transport of the phospholipid headgroups phosphoryl-ethanolamine (PE), glycerol- 1-phosphate (G1P), and glycerol-3-phosphate (G3P). The SBP MED193_10041 component of a TRAP-transporter is required for the uptake of ethanolamine, a degradation product of PE. Not only does this SBP form a new cluster within the TRAP-transporter family, but the corresponding gene was found highly expressed in the Tara Oceans metatranscriptomics database. The SBP MED193_19449 component of an ABC-transporter can bind dihydroxyacetone phosphate, an oxidation product of G1P and G3P. Furthermore, I describe the degradation pathway of phosphocholine (PC) in MED193. However, the SBP of PC or choline remains unknown. In addition, this work focused on phosphatases from MED193 and the marine phototroph Synechococcus sp. WH8102 that are required for the hydrolysis of organic P compounds. I used biochemical methods to describe these proteins and bioinformatics was deployed to identify key metals that are required for enzyme activity, confirming the requirement of an iron-calcium cluster for the activity of PhoX-type phosphatases. The combination of these methods allowed us to discover new enzymes and describe new pathways within the marine P cycle.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QH Natural history Q Science > QP Physiology
Library of Congress Subject Headings (LCSH):	Phosphorus cycle (Biogeochemistry), Marine biology -- Research, Metalloenzymes
Official Date:	October 2021
Dates:	Date Event October 2021 UNSPECIFIED
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Scanlan, David J. ; Chen, Yin ; Blindauer, Claudia A.
Extent:	vviii, 334 leaves : illustrations, charts
Language:	eng

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