The Mycoplasma gallisepticum virulence factor lipoprotein MslA is a novel polynucleotide binding protein

Although lipoproteins of mycoplasmas are thought to play a crucial role in interactions with their hosts, very few have had their biochemical function defined. The gene encoding the lipoprotein MslA in Mycoplasma gallisepticum has recently been shown to be required for virulence, but the biochemical function of this gene is not known. Although this gene has no significant sequence similarity to any gene of known function, it is located within an operon in M. gallisepticum that contains a homolog of a gene previously shown to be a nonspecific exonuclease. We mutagenized both genes to facilitate expression in Escherichia coli and then examined the functions of the recombinant proteins. The capacity of MslA to bind polynucleotides was examined, and we found that the protein bound single- and double-stranded DNA, as well as single-stranded RNA, with a predicted binding site of greater than 1 nucleotide but less than or equal to 5 nucleotides in length. Recombinant MslA cleaved into two fragments in vitro, both of which were able to bind oligonucleotides. These findings suggest that the role of MslA may be to act in concert with the lipoprotein nuclease to generate nucleotides for transport into the mycoplasma cell, as the remaining genes in the operon are predicted to encode an ABC transporter.