Essential Protein-Protein Interactions between Plasmodium falciparum Thymidylate Synthase and Dihydrofolate Reductase Domains

Shamira Shallom,Kai Zhang,Lei Jiang,Pradipsinh K Rathod

doi:10.1074/jbc.274.53.37781

Shamira Shallom, Kai Zhang + Show 2 more

Open Access

https://doi.org/10.1074/jbc.274.53.37781

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Abstract

In Plasmodium falciparum, dihydrofolate reductase and thymidylate synthase activities are conferred by a single 70-kDa bifunctional polypeptide (DHFR-TS, dihydrofolate reductase-thymidylate synthase) which assembles into a functional 140-kDa homodimer. In mammals, the two enzymes are smaller distinct molecules encoded on different genes. A 27-kDa amino domain of malarial DHFR-TS is sufficient to provide DHFR activity, but the structural requirements for TS function have not been established. Although the 3'-end of DHFR-TS has high homology to TS sequences from other species, expression of this protein fragment failed to yield active TS enzyme, and it failed to complement TS(-) Escherichia coli. Unexpectedly, even partial 5'-deletion of full-length DHFR-TS gene abolished TS function on the 3'-end. Thus, it was hypothesized that the amino end of the bifunctional parasite protein plays an important role in TS function. When the 27-kDa amino domain (DHFR) was provided in trans, a previously inactive 40-kDa carboxyl-domain from malarial DHFR-TS regained its TS function. Physical characterization of the "split enzymes" revealed that the 27- and the 40-kDa fragments of DHFR-TS had reassembled into a 140-kDa hybrid complex. Thus, in malarial DHFR-TS, there are physical interactions between the DHFR domain and the TS domain, and these interactions are necessary to obtain a catalytically active TS. Interference with these essential protein-protein interactions could lead to new selective strategies to treat malaria resistant to traditional DHFR-TS inhibitors.

Highlights

In malaria as well as many other cell types, chemotherapy targeted at dihydrofolate reductase (DHFR)1 and thymidylate synthase (TS) has proven to be highly effective [6, 7]
The Carboxyl End of Malarial DHFR-TS Is Insufficient for TS Function—The amino-terminal DHFR domain of malarial DHFR-TS can be expressed in functional form [32, 34, 37, 38], but all attempts to express the carboxyl end TS domain in a catalytically active form have been unsuccessful
When Rue10 cells are transformed with an expression plasmid coding for full-length malarial DHFR-TS gene (Fig. 1A), E. coli Rue10 proliferate even in the absence of thymidine (Fig. 1B)

Summary

Introduction

In malaria as well as many other cell types, chemotherapy targeted at dihydrofolate reductase (DHFR)1 and thymidylate synthase (TS) has proven to be highly effective [6, 7]. When Rue10 cells are transformed with an expression plasmid coding for full-length malarial DHFR-TS gene (Fig. 1A), E. coli Rue10 proliferate even in the absence of thymidine (Fig. 1B).

Results

Conclusion