This family named after a PPE motif near to the amino terminus of the domain. The PPE family of proteins all contain an amino-terminal region of about 180 amino acids. The carboxyl terminus of this family are variable, and on the basis of this region fall into at least three groups. The MPTR subgroup has tandem copies of a motif NXGXGNXG. The second subgroup contains a conserved motif at about position 350. The third group are only related in the amino terminal region. The function of these proteins is uncertain but it has been suggested that they may be related to antigenic variation of Mycobacterium tuberculosis.