A cleavable N-terminal membrane anchor is involved in membrane binding of the Escherichia coli SRP receptor.
Different from eukaryotes, the bacterial signal recognition particle (SRP) receptor lacks a membrane-tethering SRP receptor (SR) beta subunit and is composed of only the SR alpha homologue FtsY. FtsY is a modular protein composed of three domains. The N- and G-domains of FtsY are highly similar to the corresponding domains of Ffh/SRP54 and SR alpha and constitute the essential core of FtsY. In contrast, the weakly conserved N-terminal A-domain does not seem to be essential, and its exact function is unknown. Our data show that a 14-amino-acid-long positively charged region at the N-terminus of the A-domain is involved in stabilizing the FtsY-SecYEG interaction. Mutant analyses reveal that the positively charged residues are crucial for this function, and we propose that the 14-amino-acid region serves as a transient lipid anchor. In its absence, the activity of FtsY to support cotranslational integration is reduced to about 50%. Strikingly, in vivo, a truncated isoform of FtsY that lacks exactly these first 14 amino acids exists. Different from full-length FtsY, which primarily cofractionates with the membrane, the N-terminally truncated isoform is primarily present in the soluble fraction. Mutating the conserved glycine residue at position 14 prevents the formation of the truncated isoform and impairs the activity of FtsY in cotranslational targeting. These data suggest that membrane binding and function of FtsY are in part regulated by proteolytic cleavage of the conserved 14-amino-acid motif.
Weiche
Benjamin
B
Institut für Biochemie und Molekularbiologie, Zentrum für Biochemie und Molekulare Zellforschung, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany.
Bürk
Jonas
J
Angelini
Sandra
S
Schiltz
Emile
E
Thumfart
Jörg Oliver
JO
Koch
Hans-Georg
HG
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D004926:Escherichia coli / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D020033:Protein Isoforms / Q000378:metabolism; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*; D018271:Signal Recognition Particle / Q000378:metabolism*
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C087406:FtsY protein, Bacteria; D020033:Protein Isoforms; D018160:Receptors, Cytoplasmic and Nuclear; D018000:Receptors, Peptide; D018271:Signal Recognition Particle; C036318:signal peptide receptor