Abstract
The MSMEG_4306 gene from Mycobacterium smegmatis encodes a protein of unknown function with 242 amino-acid residues that contains a conserved zinc-ribbon domain at its C-terminus. Here, the crystal structure of MSMEG_4306 determined by the single-wavelength anomalous dispersion method using just one zinc ion co-purified with the protein is reported. The crystal structure of MSMEG_4306 shows a coiled-coil helix domain in the N-terminal region and a zinc-ribbon domain in the C-terminal region. A structural similarity search against the Protein Data Bank using MSMEG_4306 as a query revealed two similar structures, namely CT398 from Chlamydia trachomatis and HP0958 from Helicobacter pylori, although they share only ∼15% sequence identity with MSMEG_4306. Based on comparative analysis, it is predicted that MSMEG_4306 may be involved in secretion systems, possibly by interacting with multiple proteins or nucleic acids.
Highlights
The rapidly increasing availability of genome-sequencing data has resulted in the prediction of many protein sequences for which function cannot be assigned owing to a lack of sequence similarity to any protein with known function
Since it is difficult to predict the functions of hypothetical proteins based on sequence analysis alone, structural studies have been employed to predict the functions of hypothetical proteins (Teh et al, 2014; Shrivastava et al, 2017; da Fonseca et al, 2012; Park et al, 2012)
The MSMEG_4306 gene in Mycobacterium smegmatis encodes a protein of unknown function, and its homologue Rv2229c in M. tuberculosis has been shown to be essential for survival (Sassetti et al, 2003; Griffin et al, 2011; Xu et al, 2013)
Summary
The rapidly increasing availability of genome-sequencing data has resulted in the prediction of many protein sequences for which function cannot be assigned owing to a lack of sequence similarity to any protein with known function. These proteins are generally classified as either hypothetical or uncharacterized proteins. Proteins containing the zf-RING_7 domain are predicted to bind nucleotides/nucleic acids (Rigden, 2011), proteins or small molecules (Bouhouche et al, 2000; Eisenhaber et al, 2007; Klug, 2010; Markus & Morris, 2009; Matthews & Sunde, 2002). The crystal structure of MSMEG_4306 reveals a long coiled-coil helical domain in its N-terminal region and a zinc-ribbon domain in its C-terminal region
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