Revision as of 08:16, 10 October 2023

hemD

This is an enzyme involved in the heme biosynthetic pathway. Also called uroporphyrinogen III synthase.

IISER_Bhopal 2021

Usage and Biology

During heme biosynthesis, this enzyme catalyses the asymmetric cyclization of linear tetrapyrrole to form a uroporphyrinogen III isomer. At the catalytic site, hydroxymethylbilane use as a substrate gives uroporphyrinogen III[1]. Reports have identified that along with hemA and hemL, upregulation of hemD and hemF increases the 5-Aminolevulinic acid accumulation which is a promising source for cancer treatment[2].

References

1. Schubert, H. L., Phillips, J. D., Heroux, A., & Hill, C. P. (2008). Structure and Mechanistic Implications of a Uroporphyrinogen III Synthase−Product Complex. Biochemistry, 47(33), 8648–8655.

2. Zhang, J., Kang, Z., Chen, J., & Du, G. (2015). Optimization of the heme biosynthesis pathway for the production of 5-aminolevulinic acid in Escherichia coli. Scientific Reports, 5(1).

Sequence and Features

Jiangnan-China 2023

In our project, we divide the synthesis pathway of heme into two parts, one is the synthesis pathway of heme premise ALA, and the other part is the synthesis pathway of ALA to heme, one upstream and one downstream. For the upstream pathway, there are two pathways from glutamate to ALA, one is the C4 pathway and the other is the C5 pathway. The C4 pathway has been enhanced by the existing team, and the experimental results show that the effect is not as good as the C5 pathway, so we chose the C5 pathway for modification. The C5 pathway has two key genes, one is hemA and the other is hemL. By constructing plasmid containing hemA and hemL and transforming them, we overexpress hemA and hemL genes. The downstream pathway, that is, the synthesis pathway of heme, involves 7 genes, of which 4 genes (hemB, hemD, hemC, hemH) are more critical, according to the literature. Therefore, we also constructed plasmid to overexpress hemB, D, C, and H.

Fig1: Heme biosynthetic pathways in E. coli. The purple arrow represents the C5 pathway and the pink arrow represents the downstream biosynthetic pathway of heme. The pCDFDuet-hemA-hemL plasmid was constructed to enhance C5 pathway; the pETDuet-hemBDC-hemH plasmid was constructed to enhance downstream biosynthetic pathway

Therefore, 3 recombinant strains are constructed, E. coli AL strain(The recombinant plasmid pCDFDuet-hemA-hemL is expressed in E. coli O2), E. coli BCDH strain (The recombinant plasmid pETDuet-hemB-hemC-hemD-hemH is expressed in E. coli O2), E. coli AL-BCDH strain(The recombinant plasmids pCDFDuet-hemA-hemL and pETDuet-hemB-hemC-hemD-hemH are expressed in E. coli O2).

Fig2: The color of engineered strains and pure enzyme. 1: E. coli O1 strain; 2: E. coli O2 strain; 3: E. coli O2 strain cultivated with ALA and FeCl3; 4: E. coli AL strain; 5: Olep enzyme purified from E. coli AL strain. The lower values represent the content of intracellular heme in different engineered strains

The experimental results showed that, without the addition of ALA and FeCl3, the heme binding rate of Olep increased to 53.9%, and the conversion rate of deoxycholic acid increased to 41.4%.

Fig3: The effect of enhancing heme biosynthesis on the Olep catalysis