Proteomics of Mycoplasma genitalium: identification and characterization of unannotated and atypical proteins in a small model genome

We present the results of a comprehensive analysis of the proteome of Mycop lasma genitalium (MG), the smallest autonomously replicating organism that has been completely sequenced, Our aim was to identify and characterize all soluble proteins in MG that are structurally and functionally uncharacteri zed. We were particularly interested in identifying proteins that differed significantly from typical globular proteins, for example, proteins which a re unstructured in the absence of a 'partner' molecule or those that exhibi t unusual thermodynamic properties. This work is complementary to other str uctural genomics projects whose primary aim is to determine the three-dimen sional structures of proteins with unknown folds. We have identified all th e full-length open reading frames (ORFs) in MG that have no homologs of kno wn structure and are of unknown function. Twenty-five of the total 483 ORFs fall into this category and we have expressed, purified and characterized 11 of them. We have used circular dichroism (CD) to rapidly investigate the ir biophysical properties. Our studies reveal that these proteins have a wi de range of structures varying from highly helical to partially structured to unfolded or random coil. They also display a variety of thermodynamic pr operties ranging from cooperative unfolding to no detectable unfolding upon thermal denaturation, Several of these proteins are highly conserved from mycoplasma to man. Further information about target selection and CD result s is available at http://bioinfo.mbb.yale.edu/genome.