Dr Andrew Lawrence- University of Southampton
Dr Tracy Nissan – University of Southampton
Vitamin B12 (cobalamin) is an essential micronutrient whose synthesis is restricted to only certain bacteria.
It consists of a cobalt-containing corrin ring and a lower base attached via the nucleotide loop. It is one of the most complex molecules found in Nature. In fact, cobalamin actually belongs to a large family of related molecules that differ in the nature of the base which forms the lower ligand to the cobalt. From biological isolates, around 24 different substituents in this position have been identified. Most commonly they range from benzimidazoles, purine derivatives and aromatics such as phenol, giving rise to a huge diversity in the lower loop region of the cofactor.
The chemical variability present in this key nutrient highlights the important role which cobalamin plays in complex bacterial communities for example in the microbiome but also in soil and marine ecosystems. The aims of this project are to investigate the biosynthesis of the different purine derivatives of cobalamin, primarily 2-methyladenine and 2-methylthioadenine. These unusual base modifications have been observed in tRNA and appear to be part of a broader regulatory mechanism. The different adenine analogues likely a reflect specific status within many bacteria cells and could represent singalling across communities. In this project we will: 1. Investigate the modification of adenine bases, the enzymes responsible (eg.MiaB), and the conditions underwhich these processes are activatied. 2. Investigate the pathway and generation of free nucleotides from tRNAs to be processed into further into free modified bases. 3. Incorporation of the modified bases into cobalamin. Free bases are first activated by a phosphoribosyl transferase (CobT). The specificity of the activation system towards a range of adenine derivatives will also be investigated. 4. Examine the relationship between the synthesis of B12 varients and symbiotic/competitive interactions in bacterial communities, eg. Soil bacteria communities which can influence agricultural yield and disease.