A particular evolutionary story for Trypanosoma aquaporins
Some trypanosomatid Major Intrinsic Proteins (MIPs) mediate the uptake of antiparasitic compounds. We got insight into the diversity of these channels among Kinetoplastids and expose that trypanosomatid aquaporins (AQPs) integrate a distant cluster from all the currently defined MIP families.
MIPs are channels embedded in biological membranes that can be found in most forms of life. Maybe you´ve never heard about MIPs but for sure you´ve heard about AQPs and aquaglyceroporins. The term MIP refers to the complete protein superfamily, today integrated by more than 60,000 sequences. Near to three decades ago MIP proteins were identified as water channels. Today, we know that there is a vast diversity of MIP channels, some of them facilitate the diffusion of water, others the diffusion of glycerol or small solutes like urea, metalloids, or ions. We well know that some channels facilitate the diffusion of a lot of solutes. Still, there are channels that we have no idea what they permeate. This is the first interesting point about them but wait, there is more.
Since MIPs were discovered, plant and mammals MIPs have been subject of study because of their role in various physiological process. As it is understandable in the field of plant biology, the studies focused mostly on MIP water transport capabilities. Whereas mammals’ channels were investigated as they are involved in many physiological processes, for example in kidney formation of a concentrated urine and in pathophysiological events like nephrogenic diabetes insipidus and brain edema. But here, in this paper, we focus in trypanosomatid MIPs, why?
Trypanosoma cruzi causes Chagas disease, a zoonotic infectious that is still problematic in Latin America. The chemotherapy is effective only in acute phases of the diseases and is less effective with patients aging. Therefore, it would be great to get more potential targets of anti-protozoal drugs. T. brucei AQP2 and Leishmania spp. AQP1 mediate the uptake of antiparasitic compounds, and their down regulation or mutation lead to resistance events. What happens with other Trypanosoma MIPs? Would it be possible to design drugs targeting their MIPs?
Having all this into account Dr. Alleva conceived a project to characterize T. cruzi AQPs and Dr. Tesan was the postdoc in charge of start cloning them as well as structurally analyze them. By those days I arrived to Allevas’s lab to work on structural determinants of a plant aquaporin (nothing to do with Trypanosoma). As part of the first description, the idea was to build a phylogenetic tree of all Trypanosoma AQPs and at that point I joined the project. But it was not possible to create a nice phylogenetic tree including all trypanosomatid MIPs as I was used to. And there we realize that, even if some trypanosome MIPs are important (at least for the research community), a thorough study of their diversity was missing. And just like that, our paper was born.
Enthusiastic and quickly learning about phylogenetics, Dr. Tesan started working in this evolutionary study of kinetoplastids MIPs. We looked for Discoba MIPs digging in public databases to find a root for the phylogenetic tree only to find nothing. To look among other protists made evolutionary no sense for us. And at that point we decided to construct a sequence similarity network (SSN) of the complete MIP superfamily. The SSN was really a nice tool to observe MIPs diversity and gave us confidence to suggest the presence of trypanosomatid MIPs in a cluster far away of the already nicely characterized MIP groups. Moreover, trypanosomatid MIPs cluster with prokaryotic uncharacterized MIPs. Then, we decided to look in all the available genome and transcriptome assemblies. At that time, our collaborator Dr. Ramiro Lorenzo joined us to assist with the genome and transcriptome assemblies and the synteny studies. Also, different researchers working on kinetoplastids gave us access to their data, and we are truly thankful to them.
We think that we were able to put a lot of pieces together exposing the diversity of trypanosomatid MIPs and we are glad of that. Still, we believe that the puzzle is far from being complete. An interesting and beautiful thing is that, even if inside the MIP superfamily the amino acid sequence identity is very low, all these channels share a typical three-dimensional structure of hourglass with specific regions of filters already described to be important to the solute selectivity. In our paper we described which are these residues in trypanosome AQPXs. From here there is still a lot of work to do, the nature of biologically relevant solutes that permeate these channels is still elusive and to find them may assist drug design.
Dr. Alleva and I, we both have research stories connected to plant MIPs. So, what are we doing here?
Well, we are open minded. Karina Alleva loves biophysics and structure elucidation in these channels is a new and exciting challenge and as for me, I just love evolution and phylogeny. And with trypanosome MIPs we had a lot of material to prepare a nice party to share with the research community. We hope you enjoy it. And importantly we hope someday we will understand the transport capabilities of American trypanosome MIPs.
Click here to find our paper "AQPX-cluster aquaporins and aquaglyceroporins are asymmetrically distributed in trypanosomes"