Membrane Topology of the 12- and the 25-kDa Subunits of the Mammalian Signal Peptidase Complex

摘要: Abstract The cleavage of signal sequences secretory and membrane proteins by the peptidase complex occurs in lumen endoplasmic reticulum. Mammalian consists five subunits. Four have been cloned, SPC18, SPC21, SPC22/23, SPC25, which all but SPC25 demonstrated to be single-spanning exposed We determined cDNA sequence remaining 12-kDa subunit (SPC12) as well topologies SPC12 rough microsomes. Both polypeptides span twice with their N C termini facing cytosol contain only very small, if any, lumenal domains. Therefore, are likely involved processes other than enzymatic sequence.