Functional characterization of the ubiquitin-domain protein N_mag2608 of the haloalkaliphilic archaeon Natrialba magadii

SOLCHAGA, JI; ORDOÑEZ, M. V.; NERCESSIAN, D.

Córdoba

Congreso; XI Congreso de la Sociedad Argentina de Microbiología General; 2015

Sociedad Argentina de Microbiología General

Ubiquitin isa small and extremely well conserved protein among the Eukarya domain but absentin the other two domains of life. It is transiently attached to differentproteins where it regulates several cellular functions. Ubiquitin (Ub) displays a stable β-grasp fold and exhibit a conserved di-glycine motifin its C-terminus, essential to exert its function. Although Ub is restrictedto eukaryotes, a superfamily of ubiquitin-like (Ubl) proteins is known to bepresent in all domains of life. In general, this group of proteins do not sharehigh sequence identity with Ub, however, they display the β-grasp fold and often have the C-terminal di-glycinemotif. The ubiquitin fold has also been found in larger multidomain proteins called Ubiquitin-likeDomain-containing proteins (Ulds). They do not bind covalently with otherproteins, however they can form non-covalent interactions with proteinscontaining either ubiquitin-associated or ubiquitin-like binding domains.Nmag_2608 is an Uld protein ofthe haloalkaliphilic archaeon Natrialba magadii.It was previously identified and characterized in our laboratory as anextracellular protein with an ubiquitin-like domain, called P400. This proteinis expressed and secreted to the extracellular medium specifically in earlystationary phase. The aim of this work was to identify the physiological roleof Nmag_2608 and the importance ofP400 domain. For this, the ubiquitin domainP400 was heterologously expressed in E. coli and its purification wasoptimized. Given the extracellular localization of the protein, the possibilityof an antimicrobial activity by P400r was evaluated. The detection of thisactivity was analyzed by growth inhibition of different microorganisms inliquid medium under the presence of P400. Results shown here describe thisanalysis performed with 8 different halophilic microorganisms and two bacterialstrains. We found that P400 exhibit antimicrobial activity against a diverserange of microorganism belonging to the haloarchaea family. None of thebacterial strains tested was sensible to the presence of P400. Also, ourresults indicate different degree of inhibition within haloarchaea species. Thereason for this difference will be further analyzed, but they may be due to amore specific action of the molecule against microorganisms more commonly foundin the same environment that Natrialba magadii. These results suggest thatextracellular domain P400 of Nmag_2608 would act as antimicrobial peptide,regulating the competence with other microorganisms from its naturalenvironment and giving Natrialba magadii an ecological advantage. This isthe first report of an Ubiquitin-like domain protein with antimicrobialactivity.Supported by CONICET and UNMdP.