Towards a comparative anatomy of N-terminal topogenic protein sequences

A comparative study of three kinds of eukaryotic N-terminal topogenic sequences, viz signal peptides, N-terminal transmembrane anchors, and mitochondrial targeting sequences, suggests: (1) that the sign of the N-terminal charge might influence the orientation of an N-terminal hydrophobic segment relative to the membrane and give rise to N-terminally anchored proteins with their main mass exposed either on the cytosolic or extra-cytosolic side of the membrane; and (2) that N-terminal transmembrane segments in mitochondrial targeting sequences have a relatively low overall hydrophobicity, probably in order to avoid being recognized by the endoplasmic reticulum export machinery.