Structural and phylogenetic analysis of a conserved actinobacteria-specific protein (ASP1; SCO1997) from Streptomyces coelicolor

Here we report the first characterization of one of the 5 actinobacteria-specific proteins, ASP1 (Gene ID: SCO1997) from Streptomyces coelicolor. The X-ray crystal structure of ASP1 was determined at 2.2 ？. The overall structure of ASP1 retains a similar fold to the large NP-1 family of nucleoside phosphorylase enzymes; however, the function is not related. Further comparative analysis revealed two regions expected to be important for protein function: a central, divalent metal ion binding pore, and a highly conserved elbow shaped helical region at the C-terminus. Sequence analyses revealed that ASP1 is paralogous to another actinobacteria-specific protein ASP2 (SCO1662 from S. coelicolor) and that both proteins likely carry out similar function.Our structural data in combination with sequence analysis supports the idea that two of the 5 actinobacteria-specific proteins, ASP1 and ASP2, mediate similar function. This function is predicted to be novel since the structures of these proteins do not match any known protein with or without known function. Our results suggest that this function could involve divalent metal ion binding/transport.Actinobacteria constitute one of the main phyla within the Bacteria and they are highly diverse in terms of their morphology, physiology and ecology [2-5]. These bacteria are characterized by high G+C content (greater than 55 mol%) [3,4] and a monoderm cell structure (i.e. bounded by a single membrane)[6,7]. They include Streptomyces, the major antibiotic producers in the pharmaceutical industry as well as many important human, animal and plant pathogens, such as Mycobacterium, Tropheryma, Nocardia, Propionibacterium, Leifsonia, etc. However, except for their clustering in the 16S rRNA tree, no molecular, biochemical or physiological characteristics are known that can clearly distinguish species belonging to the phylum Actinobacteria from other bacteria [8,9].Comparative analyses of genomic sequences are enabling identification of n