Sequence analysis of a 50 kDa Natronococcus occultus Protein that Reacts with Anti-Ubiquitin Antibody

ORDOÑEZ MV; NERCESSIAN D; CONDE RD

Rosario

Congreso; LII Reunion Annual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2006

Sociedad Argentina de Investigación Bioquímica y Biología Molecular

Both eukaryotic and prokaryotic organisms contain ubiquitin-like proteins. In most eukaryotic cells, ubiquitin appears as a multiubiquitin chain or as a fusion protein of different ribosomal proteins. We have previously reported data suggesting the presence of ubiquitin?like proteins in halophilic archaea. This work reports the isolation by 2D SDS-PAGE of a 50 kDa and pI 3.1 protein from Natronococcus occultus. It reacted with antibodies against ubiquitin and, like proteins of the ubiquitin family, is heat-stable. After its in-gel digestion with trypsin, the resulting peptides were analyzed by MALDI-TOF. In spite of the scarce data available of protein sequences of haloalkaliphilic microorganisms, alignment of the peptide mass fingerprint showed significant score with two proteins. One is the Signal Recognition Protein 54 (SRP54) from Archaeoglobus fulgidus of 48.2 kDa and pI of 9.03. The other is a Ribosomal Proteins L11p from Pyrococcus abissy of 17.74 kDa and pI 6.02. Likeness to more than one protein of the same spot suggests presence of a conjugation complex even when size and pI of individual proteins not agree with those found. Differences may be linked to either aminoacidic composition or loss of fragments during conjugation. The presence of the L11p ribosomal protein is consistent with our previous studies describing the presence proteins reactive with antiubiquitin antibodies in Ncc. occultus ribosomes. The significance of presented results in protein metabolism must be further studied. [This work was supported by CONICET and UNMdP].