Consensus analysis of signal peptide peptidase and homologous human aspartic proteases reveals opposite topology of catalytic domains compared with presenilins.
The human genome encodes seven intramembrane-cleaving GXGD aspartic proteases. These are the two presenilins that activate signaling molecules and are implicated in Alzheimer's disease, signal peptide peptidase (SPP), required for immune surveillance, and four SPP-like candidate proteases (SPPLs), of unknown function. Here we describe a comparative analysis of the topologies of SPP and its human homologues, SPPL2a, -2b, -2c, and -3. We demonstrate that their N-terminal extensions are located in the extracellular space and, except for SPPL3, are modified with N-glycans. Whereas SPPL2a, -2b, and -2c contain a signal sequence, SPP and SPPL3 contain a type I signal anchor sequence for initiation of protein translocation and membrane insertion. The hydrophilic loops joining the transmembrane regions, which contain the catalytic residues, are facing the exoplasm. The C termini of all these proteins are exposed toward the cytosol. Taken together, our study demonstrates that SPP and its homologues are all of the same principal structure with a catalytic domain embedded in the membrane in opposite orientation to that of presenilins. Other than presenilins, SPPL2a, -2b, -2c, and -3 are therefore predicted to cleave type II-oriented substrate peptides like the prototypic protease SPP.
Friedmann
Elena
E
Institute of Biochemistry, Swiss Federal Institute of Technology (ETH), ETH-Hoenggerberg, 8093 Zurich, Switzerland.
Lemberg
Marius K
MK
Weihofen
Andreas
A
Dev
Kumlesh K
KK
Dengler
Uwe
U
Rovelli
Giorgio
G
Martoglio
Bruno
B
D016282:Aspartic Acid Endopeptidases / Q000737:chemistry*; D001665:Binding Sites; D015153:Blotting, Western; D002384:Catalysis; D020134:Catalytic Domain; D002460:Cell Line; D002474:Cell-Free System; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D019084:Fluorescent Antibody Technique, Indirect; D015723:Gene Library; D006031:Glycosylation; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D010957:Plasmids / Q000378:metabolism; D011134:Polysaccharides / Q000737:chemistry; D053764:Presenilin-1; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D012333:RNA, Messenger / Q000378:metabolism; D014018:Tissue Distribution; D014158:Transcription, Genetic
D018076:DNA, Complementary; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D011134:Polysaccharides; D053764:Presenilin-1; D012333:RNA, Messenger; D016282:Aspartic Acid Endopeptidases; C460085:signal peptide peptidase