Membrane topology of the Streptomyces lividans type I signal peptidases.
Most bacterial membranes contain one or two type I signal peptidases (SPases) for the removal of signal peptides from export proteins. For Streptomyces lividans, four different type I SPases (denoted SipW, SipX, SipY, and SipZ) were previously described. In this communication, we report the experimental determination of the membrane topology of these SPases. A protease protection assay of SPase tendamistat fusions confirmed the presence of the N- as well as the C-terminal transmembrane anchor for SipY. SipX and SipZ have a predicted topology similar to that of SipY. These three S. lividans SPases are currently the only known prokaryotic-type type I SPases of gram-positive bacteria with a C-terminal transmembrane anchor, thereby establishing a new subclass of type I SPases. In contrast, S. lividans SipW contains only the N-terminal transmembrane segment, similar to most type I SPases of gram-positive bacteria. Functional analysis showed that the C-terminal transmembrane anchor of SipY is important to enhance the processing activity, both in vitro as well as in vivo. Moreover, for the S. lividans SPases, a relation seems to exist between the presence or absence of the C-terminal anchor and the relative contributions to the total SPase processing activity in the cell. SipY and SipZ, two SPases with a C-terminal anchor, were shown to be of major importance to the cell. Accordingly, for SipW, missing the C-terminal anchor, a minor role in preprotein processing was found.
Geukens
N
N
Laboratory of Bacteriology, Rega Institute, Katholieke Universiteit Leuven, 3000 Leuven, Belgium.
Lammertyn
E
E
Van Mellaert
L
L
Schacht
S
S
Schaerlaekens
K
K
Parro
V
V
Bron
S
S
Engelborghs
Y
Y
Mellado
R P
RP
Anné
J
J
D001483:Base Sequence; D002462:Cell Membrane / Q000201:enzymology; D017931:DNA Primers; D006094:Gram-Positive Bacteria / Q000201:enzymology; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010957:Plasmids; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012697:Serine Endopeptidases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013302:Streptomyces / Q000201:enzymology* / Q000235:genetics
D017931:DNA Primers; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D012697:Serine Endopeptidases; C026515:type I signal peptidase