The Relationship between Functional and Evolutionary Correlations of Enzyme Reactions in Metabolic Network Evolution

Abstract The evolution of species is inevitably accompanied by the evolution of metabolic networks to adapt to different environments. The metabolic networks of different species were collected from the Kyoto Encyclopedia of Genes and Genomes (KEGG) website, and some enzyme reactions with the highest occurrence frequency in all species were found and are reported in this paper. The correlation coefficients of whether the enzyme reactions appear in all species were calculated, and the corresponding evolutionary correlation connection networks were calculated according to different correlation coefficient thresholds. These studies show that, as the evolutionary correlation of enzyme reactions increases, the weighted average of the mean functional concentration ratios of the enzyme reactions also increases, indicating that the functional concentration ratio of enzyme reactions has a certain correlation with the evolutionary correlation. The work presented in this paper enhances our understanding of the characteristics and general rules of metabolic network evolution.

Purification and characterization of S-adenosyl-L-methionine:uroporphyrinogen Ⅲ methyltransferase from Rhodobacter capsulatus SB1003 / 生物工程学报

Biosynthesis of vitamin B₁₂ (VB₁₂) requires the methylation at positions C-2 and C-7 of the precursor uroporphyrinogen Ⅲ (urogen Ⅲ) to precorrin-2 by S-adenosyl-L-methionine uroporphyrinogen Ⅲ methyltransferase (SUMT), which is a potential bottleneck step. Most of SUMTs are inhibited by urogen Ⅲ and by-product S-adenosyl-L-homocysteine (SAH). In order to mine an SUMT that lacks such an inhibitory property to drive greater flux through the VB₁₂ biosynthetic pathway, we cloned two SUMT genes (RCcobA1, RCcobA2) from Rhodobacter capsulatus SB1003 and expressed them in Escherichia coli BL21 (DE3). Thereafter, the two enzymes were purified and their specific activity of 27.3 U/mg, 68.9 U/mg were determined respectively. The latter was 2.4 times higher than PDcobA (27.9 U/mg) from Pseudomonas denitrifican. Additionally, RCcobA2 could tolerate over 70 μmol/L urogen Ⅲ, which has never been reported before. Hence, RCcobA2 can be used as an efficient enzyme to regulate the VB₁₂ metabolic pathway and enhance VB₁₂ production in industrial strains.