CONICET | Buscador de Institutos y Recursos Humanos

Ubiquitin is a small and extremely well conserved protein among theEukarya domain but absent in the other two domains of life. It is transientlyattached to different proteins where. It regulates several cellular functions.Ubiquitin (Ub) displays a stable β-graspfold and exhibit a conserved di-glycine motif in its C-terminus, essential toexert its function. Although Ub is restricted to eukaryotes, a superfamily ofubiquitin-like (Ubl) proteins is known to be present in all domains of life. Ingeneral, this group of proteins do not share high sequence identity with Ub,however, they display the β-graspfold and often have the C-terminal di-glycine motif. The ubiquitin fold hasalso been found in larger multi domain proteins called Ubiquitin-like Domain-containingproteins (Ulds). They do not bind covalently with other proteins, however theycan form non-covalent interactions with proteins containing eitherubiquitin-associated or ubiquitin-like binding domains. Nmag_2608 is an Uldprotein of the haloalkaliphilic archaeon Natrialba magadii. It was previouslyidentified and characterizedin our laboratory as an extracellular protein withan ubiquitin-like domain, called P400. This protein is expressed and secretedto the extracellular medium specifically in early stationary phase. The aim ofthis work was to identify the physiological role of Nmag_2608 and theimportance of P400 domain. For this, the ubiquitin domain P400 washeterologously expressed in E. coli and its purification was optimized. Given theextracellular localization of the protein, the possibility of an antimicrobialactivity by P400r was evaluated. The detection of this activity was analyzed bygrowth inhibition of different microorganisms in liquid medium under thepresence of P400. Results shown here describethis analysis performed with 8different halophilic microorganisms and two bacterial strains. We found that P400exhibit antimicrobial activity against a diverse range of microorganismbelonging to the haloarchaea family. None of the bacterial strains tested wassensible to the presence of P400. Also, our results indicate different degreeof inhibition within haloarchaea species. The reason for this difference willbe further analyzed, but they may be due to a more specific action of the moleculeagainst microorganisms more commonly found in the same environment that Natrialbamagadii.These results suggest that extracellular domain P400 of Nmag_2608 wouldact as antimicrobial peptide, regulating the competence with other microorganismsfrom its natural environment and giving Natrialba magadii an ecologicaladvantage. This is the first report of an Ubiquitin-like domain protein withantimicrobial activity.