Towards functional repertoire of the earliest proteins

Abstract

The conserved protein sequence motifs present in all prokaryotic proteomes, “omnipresent motifs,” presumably, correspond to the earliest proteins of the Last Universal Cellular Ancestor, from which all the proteomes have descended. Fifteen proteomes, each representing one of the total 15 diverse phyla of 131 Eubacteria and Archea, from which the omnipresent elements have been originally derived, are exhaustively screened. All those proteins which harbor the omnipresent motifs are identified. Six “omnipresent” protein types are revealed which are located in all 15 proteomes: ABC cassettes, FtsH proteases, translation initiation factors, translation elongation factors, isoleucyl-tRNA synthases, and RNA polymerases β’. In addition to the omnipresent motifs, these proteins also contain other highly conserved motifs, standing for additional modules of the proteins. Remarkably, the identified tentative earliest proteins are responsible for only three basic functions: supply of monomers (ABC transporters and proteases), protein synthesis (initiation and elongation factors, aminoacyl-tRNA synthases), and RNA synthesis (polymerases). No enzymes involved in metabolic activities are present in the list of the earliest proteins derived by this approach. Some of the omnipresent sequence motifs are found, indeed, in the metabolic enzymes (e.g. NTP binding motifs), but these enzymes do not make a sequence matching collection of 15 sequences, i.e. they are not omnipresent. Future analysis of less conserved sequence motifs may reveal at what degree of conservation (stage of evolution) the metabolic enzymes could have entered the scene.

Keywords:

• ABC cassettes
• protein modules
• earliest proteins
• omnipresent motifs
• last universal cellular ancestor

Acknowledgments

The work has been supported by the Czech Ministry of Education (grant MSM0021622415) and by Fellowship of SoMoPro (South Moravian Program, Czech Republic) with financial contribution of European Union within the 7th framework program (FP/2007–2013, grant agreement No.229603) – for ET, and by the CAPES (Brazil) Foreign Visiting Research Fellowship PVE 0195/06–5 to YS, under supervision of RCG.