Figure 3. Crystal structure of the M.tb. PE/PPE protein complex. a) Surface representation of the PE/PPE protein complex. The PE protein Rv2431c is shown in red, and the PPE protein Rv2430c is in blue. b) The PE/PPE protein complex viewed down its longitudinal axis. c) Ribbon diagram of the PE/PPE protein complex. Regions of high sequence conservation are indicated by arrows. d) Interface hydrophobicity of the PPE and PE proteins. The hydrophobicity of the interaction interface between the PPE and PE protein is color-coded: the most apolar regions are indicated in red, orange, and yellow, and the most polar regions are indicated in blue. Structural Biology and Informatic approaches help us better investigate genomic polymorphisms and variations at the molecular and atomic levels. (Strong M. et al.Proc. Natl. Acad. Sci. U. S. A. 2006; 103:8060-8065.)