The family of M17 aminopeptidases (alias ‘leucine aminopeptidases’, M17-LAPs) utilize a highly conserved hexameric structure and a binuclear metal center to selectively remove N-terminal amino acids ...from short peptides. However, M17-LAPs are responsible for a wide variety of functions that are seemingly unrelated to proteolysis. Herein, we aimed to investigate the myriad of functions attributed to M17. Further, we attempted to differentiate between the different molecular mechanisms that allow the conserved hexameric structure of an M17-LAP to mediate such diverse functions. We have provided an overview of research that identifies precise physiological roles of M17-LAPs, and the distinct mechanisms by which the enzymes moderate those roles. The review shows that the conserved hexameric structure of the M17-LAPs has an extraordinary capability to moderate different molecular mechanisms. We have broadly categorized these mechanisms as ‘aminopeptidase-based’, which include the characteristic proteolysis reactions, and ‘association-driven’, which involves moderation of the molecule's macromolecular assembly and higher order complexation events. The different molecular mechanisms are capable of eliciting very different cellular outcomes, and must be regarded as distinct when the physiological roles of this large and important family are considered.
•M17 aminopeptidases possess a highly conserved structure and active site.•They are multifunctional, capable of performing diverse functions far beyond peptide hydrolysis.•M17 aminopeptidases from plants possess chaperone activity, while in bacteria they can bind DNA.•Here we review mechanisms that underpin the multifunctional nature of the M17 aminopeptidases.
M1 aminopeptidase enzymes are a diverse family of metalloenzymes characterized by conserved structure and reaction specificity. Excluding viruses, M1 aminopeptidases are distributed throughout all ...phyla, and have been implicated in a wide range of functions including cell maintenance, growth and development, and defense. The structure and catalytic mechanism of M1 aminopeptidases are well understood, and make them ideal candidates for the design of small‐molecule inhibitors. As a result, many research groups have assessed their utility as therapeutic targets for both infectious and chronic diseases of humans, and many inhibitors with a range of target specificities and potential therapeutic applications have been developed. Herein, we have aimed to address these studies, to determine whether the family of M1 aminopeptidases does in fact present a universal target for the treatment of a diverse range of human diseases. Our analysis indicates that early validation of M1 aminopeptidases as therapeutic targets is often overlooked, which prevents the enzymes from being confirmed as drug targets. This validation cannot be neglected, and needs to include a thorough characterization of enzymes’ specific roles within complex physiological pathways. Furthermore, any chemical probes used in target validation must be carefully designed to ensure that specificity over the closely related enzymes has been achieved. While many drug discovery programs that target M1 aminopeptidases remain in their infancy, certain inhibitors have shown promise for the treatment of a range of conditions including malaria, hypertension, and cancer.
The large family of therapeutically interesting M1 aminopeptidase enzymes has enormous potential to provide important drug targets. However, conservation of sequence, structure, and substrate specificity results in substantial challenges, and necessitates the need for careful target validation. Some studies have achieved this, and successfully validated M1 aminopeptidases as targets for the treatment of malaria, hypertension, and cancer.
The nematode Caenorhabditis elegans contains genes for two types of ferritin (ftn-1 and ftn-2) that express FTN-1 and FTN-2. We have expressed and purified both proteins and characterized them by ...X-ray crystallography, cryo-electron microscopy, transmission electron microscopy, dynamic light scattering, and kinetically by oxygen electrode and UV–vis spectroscopy. Both show ferroxidase activity, but although they have identical ferroxidase active sites, FTN-2 is shown to react approximately 10 times faster than FTN-1, with L-type ferritin character over longer time periods. We hypothesize that the large variation in rate may be due to differences in the three- and four-fold channels into the interior of the protein 24-mer. FTN-2 is shown to have a wider entrance into the three-fold channel than FTN-1. Additionally, the charge gradient through the channel of FTN-2 is more pronounced, with Asn and Gln residues in FTN-1 replaced by Asp and Glu residues in FTN-2. Both FTN-1 and FTN-2 have an Asn residue near the ferroxidase active site that is a Val in most other species, including human H ferritin. This Asn residue has been observed before in ferritin from the marine pennate diatom Pseudo-mitzchia multiseries. By replacing this Asn residue with a Val in FTN-2, we show that the reactivity decreases over long time scales. We therefore propose that Asn106 is involved in iron transport from the ferroxidase active site to the central cavity of the protein.
To combat the global burden of malaria, development of new drugs to replace or complement current therapies is urgently required. Here, we show that the compound
is a selective, nanomolar inhibitor ...of both
and
aminopeptidases M1 and M17, leading to inhibition of end-stage hemoglobin digestion in asexual parasites.
can kill sexual-stage
, is active against murine malaria, and does not show any shift in activity against a panel of parasites resistant to other antimalarials.
-resistant
exhibited a slow growth rate that was quickly outcompeted by wild-type parasites and were sensitized to the current clinical drug, artemisinin. Overall, these results confirm
as a lead compound for further drug development and highlights the potential of dual inhibition of M1 and M17 as an effective multi-species drug-targeting strategy.IMPORTANCEEach year, malaria infects approximately 240 million people and causes over 600,000 deaths, mostly in children under 5 years of age. For the past decade, artemisinin-based combination therapies have been recommended by the World Health Organization as the standard malaria treatment worldwide. Their widespread use has led to the development of artemisinin resistance in the form of delayed parasite clearance, alongside the rise of partner drug resistance. There is an urgent need to develop and deploy new antimalarial agents with novel targets and mechanisms of action. Here, we report a new and potent antimalarial compound, known as
, and show that it targets multiple stages of the malaria parasite lifecycle, is active in a preliminary mouse malaria model, and has a novel mechanism of action. Excitingly, resistance to
appears to be self-limiting, suggesting that development of the compound may provide a new class of antimalarial.
M17 leucyl aminopeptidases are metal-dependent exopeptidases that rely on oligomerization to diversify their functional roles. The M17 aminopeptidases from Plasmodium falciparum (PfA-M17) and ...Plasmodium vivax (Pv-M17) function as catalytically active hexamers to generate free amino acids from human hemoglobin and are drug targets for the design of novel antimalarial agents. However, the molecular basis for oligomeric assembly is not fully understood. In this study, we found that the active site metal ions essential for catalytic activity have a secondary structural role mediating the formation of active hexamers. We found that PfA-M17 and Pv-M17 exist in a metal-dependent dynamic equilibrium between active hexameric species and smaller inactive species that can be controlled by manipulating the identity and concentration of metals available. Mutation of residues involved in metal ion binding impaired catalytic activity and the formation of active hexamers. Structural resolution of Pv-M17 by cryoelectron microscopy and X-ray crystallography together with solution studies revealed that PfA-M17 and Pv-M17 bind metal ions and substrates in a conserved fashion, although Pv-M17 forms the active hexamer more readily and processes substrates faster than PfA-M17. On the basis of these studies, we propose a dynamic equilibrium between monomer ↔ dimer ↔ tetramer ↔ hexamer, which becomes directional toward the large oligomeric states with the addition of metal ions. This sophisticated metal-dependent dynamic equilibrium may apply to other M17 aminopeptidases and underpin the moonlighting capabilities of this enzyme family.
Plasmodium falciparum,
the causative agent of malaria, remains a global health threat as parasites continue to develop resistance to antimalarial drugs used throughout the world. Accordingly, drugs ...with novel modes of action are desperately required to combat malaria.
P. falciparum
parasites infect human red blood cells where they digest the host’s main protein constituent, hemoglobin. Leucine aminopeptidase
Pf
A-M17 is one of several aminopeptidases that have been implicated in the last step of this digestive pathway. Here, we use both reverse genetics and a compound specifically designed to inhibit the activity of
Pf
A-M17 to show that
Pf
A-M17 is essential for
P. falciparum
survival as it provides parasites with free amino acids for growth, many of which are highly likely to originate from hemoglobin. We further show that loss of
Pf
A-M17 results in parasites exhibiting multiple digestive vacuoles at the trophozoite stage. In contrast to other hemoglobin-degrading proteases that have overlapping redundant functions, we validate
Pf
A-M17 as a potential novel drug target.
Malaria is a disease spread by mosquitoes. When infected insects bite the skin, they inject parasites called
Plasmodium
into the host. The symptoms of the disease then develop when
Plasmodium
infect host red blood cells. These parasites cannot make the raw materials to build their own proteins, so instead, they digest haemoglobin – the protein used by red blood cells to carry oxygen – and use its building blocks to produce proteins.
Blocking the digestion of haemoglobin can stop malaria infections in their tracks, but it is unclear how exactly
Plasmodium
parasites break down the protein. Researchers think that a group of four enzymes called aminopeptidases are responsible for the final stage in this digestion, releasing the amino acids that make up haemoglobin. However, the individual roles of each of these aminopeptidases are not yet known.
To start filling this gap, Edgar et al. set out to study one of these aminopeptidases, called PfA-M17. First, they genetically modified
Plasmodium falciparum
parasites so that the levels of this aminopeptidase were reduced during infection. Without the enzyme, the parasites were unable to grow. The next step was to confirm that this was because PfA-M17 breaks down haemoglobin, and not for another reason. To test this, Edgar et al. designed a new molecule that could stop PfA-M17 from releasing amino acids. This molecule, which they called ‘compound 3’, had the same effect as reducing the levels of PfA-M17. Further analysis showed that the amino acids that PfA- M17 releases match the amino acids found in haemoglobin.
Malaria causes hundreds of thousands of deaths per year. Although there are treatments available, the
Plasmodium
parasites are starting to develop resistance. Confirming the role of PfA-M17 provides a starting point for new studies by parasitologists, biologists, and drug developers. This could lead to the development of chemicals that block this enzyme, forming the basis for new treatments.
Malaria remains a global health threat and growing resistance to artemisinin-based therapies calls for therapeutic agents with novel mechanisms of action. The Plasmodium spp M1 and M17 ...metalloaminopeptidases have been identified as attractive new antimalarial drug targets as inhibition of these enzymes results in antiplasmodial activity. Previously identified novel hydroxamic acid 2 as a moderate inhibitor of PfA-M1 and PfA-M17 and a potent inhibitor of P. falciparum. This study has sought to improve the enzymatic inhibitory properties in addition to increasing the drug-likeness of this scaffold by introducing polar moieties into the S1’ region of the active site. Structural biology studies on the co-crystallised structures of potent dual-inhibitor 9aa bound to PfA-M1 and PfA-M17 have revealed that there are few direct interactions between the inhibitor and the S1’ domain of these enzymes. Structure-based compound design led to the identification of a variety of novel hydroxamic acids that show improved inhibitory activity against PfA-M1 and PfA-M17, in addition to displaying antiplasmodial activity. Notably, compounds with substitutions on the aniline ring resulted in a loss of potency (Ki > 500 nM) toward PfA-M1 and PfA-M17. ioisosteric replacement of the S1-region biaryl ring system with a bromophenyl moiety resulted in increased potency compared to parent 9aa. Elaboration of 9aa to bioisosterically replace the S1 moiety with an aryl bromide, combined with substituted anilines has resulted in potent selective PfA-M1 inhibitors which show strong activity against Pf-3D7, with meta- and para-fluoroaniline groups of 15ag and 15ah forming hydrogen-bonds with residues within the active site. These findings establish the importance of the previously under-utilised S1’ domain and will aid the design of future PfA-M1 and PfA-M17 inhibitors.
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•PfA-M1 and PfA-M17 are promising antimalarial targets.•Using X-ray crystallography, a series of novel inhibitors was designed and synthesised.•Compound 9aa proved to be a potent dual-inhibitor of PfA-M1 and PfA-M17.•Compound 15aj and related analogues proved to be potent selective inhibitors of PfA-M1.•Interactions between inhibitor and S1’ are important for M1 selectivity.
There is an urgent clinical need for antimalarial compounds that target malaria caused by both Plasmodium falciparum and Plasmodium vivax. The M1 and M17 metalloexopeptidases play key roles in ...Plasmodium hemoglobin digestion and are validated drug targets. We used a multitarget strategy to rationally design inhibitors capable of potent inhibition of the M1 and M17 aminopeptidases from both P. falciparum (Pf-M1 and Pf-M17) and P. vivax (Pv-M1 and Pv-M17). The novel chemical series contains a hydroxamic acid zinc binding group to coordinate catalytic zinc ion/s, and a variety of hydrophobic groups to probe the S1′ pockets of the four target enzymes. Structural characterization by cocrystallization showed that selected compounds utilize new and unexpected binding modes; most notably, compounds substituted with bulky hydrophobic substituents displace the Pf-M17 catalytic zinc ion. Excitingly, key compounds of the series potently inhibit all four molecular targets and show antimalarial activity comparable to current clinical candidates.
The metal-dependent M17 aminopeptidases are conserved throughout all kingdoms of life. This large enzyme family is characterized by a conserved binuclear metal center and a distinctive homohexameric ...arrangement. Recently, we showed that hexamer formation in Plasmodium M17 aminopeptidases was controlled by the metal ion environment, although the functional necessity for hexamer formation is still unclear. To further understand the mechanistic role of the hexameric assembly, here we undertook an investigation of the structure and dynamics of the M17 aminopeptidase from P. falciparum, PfA-M17. We describe a novel structure of PfA-M17, which shows the active sites of each trimer are linked by a dynamic loop, and loop movement is coupled with a drastic rearrangement of the binuclear metal center and substrate-binding pocket, rendering the protein inactive. Molecular dynamics simulations and biochemical analyses of PfA-M17 variants demonstrated this rearrangement is inherent to PfA-M17, and that the transition between the active and inactive states is metal-dependent and part of a dynamic regulatory mechanism. Key to the mechanism is a remodeling of the binuclear metal center, which occurs in response to a signal from the neighboring active site and serves to moderate the rate of proteolysis under different environmental conditions. In conclusion, this work identifies a precise mechanism by which oligomerization contributes to PfA-M17 function. Furthermore, it describes a novel role for metal cofactors in the regulation of enzymes, with implications for the wide range of metalloenzymes that operate via a two-metal ion catalytic center, including DNA processing enzymes and metalloproteases.
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