Protein interaction networks for nitrate reduction in soil bacteria

Jarvis, Alexander (2020) Protein interaction networks for nitrate reduction in soil bacteria. Doctoral thesis, University of East Anglia.

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Paracoccus denitrificans is a Gram-negative model Alphaproteobacterium capable of nitrate assimilation and complete denitrification; two central pathways in the global biogeochemical nitrogen cycle. It encodes three distinct nitrate reductases, cytoplasmic Nas, respiratory Nar and periplasmic Nap. Nas supports growth through conversion of nitrate to ammonium which can be assimilated into organic molecules. Nar supports growth using nitrate as an alternative electron acceptor under anoxic conditions. Nap supports growth by reducing nitrate to remove excess electrons from the quinol-pool, produced when growth depends upon highly reduced carbon substrates. Whilst Nar and Nap have received extensive individual research the assimilatory Nas system has been comparatively under-studied.
The periplasmic nitrate reductase Nap has been shown to express strongly under growth regimes using reduced carbon substrates and thus acts as a sink for excess electrons generated by carbon metabolism. In this thesis the role of the assimilatory nitrate reductase is analysed under mixed nitrogen source conditions using continuous culture to analyse expression of nitrate reductase genes and use of carbon and nitrogen sources. The role of Nas as an alternative redox-balancing nitrate reductase with a dual assimilation function is discussed.
Previous studies have suggested a protein interaction network between three Nas proteins in P. denitrificans. These would form a total nitrate to ammonium reduction complex including the assimilatory nitrate and nitrite reductases as well as a small Rieske-type ferredoxin that facilitates electron transfer between the nitrite and nitrate reductase. This project identified novel methods for protein extraction from P. denitrificans to determine interacting partner proteins. The model for protein interactions and proposed complex forming proteins has been evolved significantly, showing a tight interaction between the nitrate reductase and a truncated form of the nitrite reductase and another tight interaction between the nitrite reductase and the Rieske-type ferredoxin. This changes the proposed role of the Rieske-type ferredoxin significantly and changes the way electron transfer in this system is understood.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Nicola Veasy
Date Deposited: 30 Mar 2022 11:14
Last Modified: 30 Sep 2023 01:38


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