Cystoisospora belli dihydrofolate reductase (DHFR) (DHFR)

Cystoisospora belli dihydrofolate reductase (DHFR) is an essential enzyme in the folate biosynthetic pathway of the protozoan parasite Cystoisospora belli, the causative agent of cystoisosporiasis (CDC, 2023). This enzyme catalyzes the NADPH-dependent reduction of 7,8-dihydrofolate to 5,6,7,8-tetrahydrofolate, which is a vital cofactor for the synthesis of thymidylate, purines, and several amino acids (NCBI, 2024). In the phylum Apicomplexa, to which C. belli belongs, DHFR is typically expressed as a bifunctional enzyme complex with thymidylate synthase (DHFR-TS) (PubMed, 2022). Because C. belli must synthesize folates de novo to support DNA replication, DHFR serves as a critical metabolic bottleneck for the parasite. Clinically, this enzyme is the primary target for antifolate medications such as trimethoprim and pyrimethamine (StatPearls, 2023). These drugs exhibit a significantly higher affinity for the parasitic enzyme compared to the human version, allowing for selective inhibition of parasite growth. Targeting DHFR is particularly important in managing opportunistic infections in immunocompromised patients, such as those with HIV/AIDS, where C. belli can cause severe, chronic diarrhea. However, the potential for developing drug resistance and the necessity for prolonged treatment courses in certain patient populations remain significant clinical considerations.

Other names

Isospora belli dihydrofolate reductaseCystoisospora belli DHFRDihydrofolate reductase-thymidylate synthaseBifunctional dihydrofolate reductase-thymidylate synthase

Competitive inhibition of the dihydrofolate reductase enzyme, which prevents the reduction of dihydrofolate to tetrahydrofolate, thereby disrupting the synthesis of thymidylate and purines necessary for DNA replication (StatPearls, 2023).