Structure of the hypothetical Mycoplasma protein MPN555 suggests a chaperone function

The crystal structure of the hypothetical protein MPN555 from Mycoplasma pneumoniae (gi|1673958) has been determined to a resolution of 2.8 Å using anomalous diffraction data at the Se-peak wavelength. Structure determination revealed a mostly α-helical protein with a three-lobed shape. The three lobes or fingers delineate a central binding groove and additional grooves between lobes 1 and 3 and between lobes 2 and 3. For one of the molecules in the asymmetric unit, the central binding pocket was filled with a peptide from the uncleaved N-terminal affinity tag. The MPN555 structure has structural homology to two bacterial chaperone proteins: SurA and trigger factor from Escherichia coli. The structural data and the homology to other chaperone proteins suggests an involvement in protein folding as a molecular chaperone for MPN555.