Abstract
BackgroundThe Actinobacteria phylum represents one of the largest and most diverse groups of bacteria, encompassing many important and well-characterized organisms including Streptomyces, Bifidobacterium, Corynebacterium and Mycobacterium. Members of this phylum are remarkably diverse in terms of life cycle, morphology, physiology and ecology. Recent comparative genomic analysis of 19 actinobacterial species determined that only 5 genes of unknown function uniquely define this large phylum [1]. The cellular functions of these actinobacteria-specific proteins (ASP) are not known.ResultsHere 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 Ǻ. 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.ConclusionOur 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.
Highlights
The Actinobacteria phylum represents one of the largest and most diverse groups of bacteria, encompassing many important and well-characterized organisms including Streptomyces, Bifidobacterium, Corynebacterium and Mycobacterium
The genes flanking ASP1 in different actinobacterial genomes are either of unknown function or perform unrelated functions
We report the structure of the first actinobacteriaspecific protein
Summary
The Actinobacteria phylum represents one of the largest and most diverse groups of bacteria, encompassing many important and well-characterized organisms including Streptomyces, Bifidobacterium, Corynebacterium and Mycobacterium. 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 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]. These proteins provide novel and useful molecular markers for this diverse group of bacteria [1] Among these actinobacteria-specific proteins, five proteins (corresponding to ML1009, ML1306, ML1029, ML0257 and ML0642 from the genome of Mycobacterium leprae TN) were found in every sequenced actinobacterial species [1] including those from the deepest branch Rubrobacter xylanophilus and from intracellular pathogens such as Tropheryma whipplei which have highly reduced genomes [9,15]. These studies are expected to provide novel insights into biochemical processes and physiological characteristics that are unique to actinobacteria
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