Allosteric regulation accompanied by oligomeric state changes of Trypanosoma brucei GMP reductase through cystathionine-β-synthase domain

Abstract

Guanosine 5′-monophosphate reductase (GMPR) is involved in the purine salvage pathway and is conserved throughout evolution. Nonetheless, the GMPR of Trypanosoma brucei (TbGMPR) includes a unique structure known as the cystathionine-β-synthase (CBS) domain, though the role of this domain is not fully understood. Here, we show that guanine and adenine nucleotides exert positive and negative effects, respectively, on TbGMPR activity by binding allosterically to the CBS domain. The present structural analyses revealed that TbGMPR forms an octamer that shows a transition between relaxed and twisted conformations in the absence and presence of guanine nucleotides, respectively, whereas the TbGMPR octamer dissociates into two tetramers when ATP is available instead of guanine nucleotides. These findings demonstrate that the CBS domain plays a key role in the allosteric regulation of TbGMPR by facilitating the transition of its oligomeric state depending on ligand nucleotide availability.

Development of therapeutic agents for human African trypanosomiasis

“…Some enzymes with the CBS domain are known to regulate activity through purine nucleotide binding to this domain [44]. A recent study demonstrated that TbGMPR has an oligomeric conformation with allosteric regulation via the CBS domain [45]. The binding of guanine nucleotides (GTP or GMP) and adenine nucleotides (ATP) to an allosteric regulatory site, formed at the cleft between the catalytic and CBS domains, leads to positive and negative regulation, respectively, accompanied by changes in the multimeric enzyme structure (Fig.…”

“…The binding of guanine nucleotides (GTP or GMP) and adenine nucleotides (ATP) to an allosteric regulatory site, formed at the cleft between the catalytic and CBS domains, leads to positive and negative regulation, respectively, accompanied by changes in the multimeric enzyme structure (Fig. 5) [45]. Specifically, TbGMPR with a "relaxed octamer" conformation in the apo form is transformed into an active "twisted octamer" by binding to GTP or GMP, while the binding of ATP disrupts the octamer structure to dissociate into two inactive tetramers.…”

“…These findings indicate that alterations in the oligomeric states of TbGMPR are responsible for allosteric regulation by purine nucleotide binding to the CBS domain. The GMPR of T. brucei is distinct from that of the host organisms due to the presence of the CBS domain [41,45]; therefore, the allosteric site in the CBS domain of TbGMPR could be a suitable therapeutic target for African trypanosomiasis. The purine nucleotide analog ribavirin 5′-monophosphate (RMP) and its nucleoside form ribavirin (Fig.…”

The mycobacterial guaB1 gene encodes a guanosine 5’-monophosphate reductase with a cystathione-β-synthase domain

“…Trypanosoma brucei GMPR is the only known GMPR structure that contains CBS domains (Imamura et al, 2020). The presence of CBS domains in GMPRs is unusual.…”

“…GMPRs typically do not possess CBSs, with the exception of GMPRs from the pathogenic protozoans Trypanosoma brucei (Tb GMPR) (Bessho et al, 2016), Trypanosoma congolense (Tc GMPR) (Sarwono et al, 2017) and Leshmania donovani (Ld GMPR) (Smith et al, 2016). Recently, structural analysis of Tb GMPR showed that ATP induces octamer dissociation, while guanine nucleotides do not influence the enzyme's oligomeric state (Imamura et al, 2020).…”