Figure 1: Pectin methylesterase(PME) structural motifs. Type I and Type II PMEs possess a conserved PME domain with characteristic, highly conserved amino acid fragments. Type I PMEs possess an N-terminal extension designated the PRO domain and a processing motif (PM) that might be a putative target for subtilisin like proteases. The targeting to the endomembrane system leading to the export of PMEs to the cell wall is mediated either by a signal peptide (SP) or a transmembrane domain (TM or signal anchor). Different PMEs possess one, both, or neither of these motifs.