Assessing the halophilic character of ADP-dependent sugar kinases from the archeon order Methanosarcinales

Halophilic organisms have evolved to live in environments of high salinity, therefore theirmolecular machinery has adapted to carry out its functions in presence of molar concentrations ofsalt. Most of the work aimed to understand the structural adaptations of these proteins has beendone using proteins from the archeon class Halobacteria. Proteins from these organisms arecharacterized by a low abundance of basic residues and a high amount of acidic residues, whichaccumulate on the protein surface, coupled with a reduction of bulky hydrophobic residues in itscore [1]. Nevertheless, halophilic organisms have been reported in a wide variety of taxa, includingother archaea orders, which their adaptation mechanisms have not been explored. To evaluate theubiquity of the protein structural adaptations found in Halobacteria, we built homology modelsof ADP-dependent kinases from halophilic and non-halophilic organisms of the archaeal orderMethanosarcinales and compared them to models from Halobacterial and Eucariotic proteins.Our results show that proteins from halophilic organisms of the Methanosarcinales order do notshow the classical bias in amino acid composition observed in Halobacteria, like the reduction ofthe hydrophobic core and negative surface charge. However, experimental characterization of theADP-dependent phosphofructokinase of the halophilic organism Methanohalobium evestigatum(from Methanosarcinales order) confirmed that the protein is indeed halotolerant, and thischaracter can be further exacerbated in presence of osmolytes commonly found on halophilicarchaea, like betaine [2]. These results suggest that the adaptations required to maintain thestructure and function of a protein in extreme salt concentrations can vary widely betweendifferent organisms. These adaptations do not rely exclusively on the amino acidic composition,being instead a product of the coevolutionary process between the protein and its intracellularenvironment. Fondecyt 1150460 References [1] Graziano, G., a Merlino, A. (2014). Molecular bases of protein halotolerance. Biochimica et Biophysica Acta(BBA) - Proteins and Proteomics, 1844(4), 850–858[2] Sowers, K. R., a Gunsalus, R. P. (1995). Halotolerance in Methanosarcina spp.: Role of N (sup (epsilon))-Acetyl-(beta)-Lysine,(alpha)-Glutamate, Glycine Betaine, and K (sup+) as Compatible Solutes for OsmoticAdaptation. Applied and environmental microbiology, 61(12), 4382-4388.