Sequence-specific interactions of nascent Escherichia coli polypeptides with trigger factor and signal recognition particle.
As nascent polypeptides exit the ribosomal tunnel they immediately associate with chaperones, folding catalysts, and targeting factors. These interactions are decisive for the future conformation and destination of the protein that is being synthesized. Using Escherichia coli as a model organism, we have systematically analyzed how the earliest contacts of nascent polypeptides with cytosolic factors depend on the nature and future destination of the emerging sequence using a photo cross-linking approach. Together, the data suggest that the chaperone trigger factor is adjacent to emerging sequences by default, consistent with both its placement near the nascent chain exit site and its cellular abundance. The signal recognition particle (SRP) effectively competes the contact with TF when a signal anchor (SA) sequence of a nascent inner membrane protein appears outside the ribosome. The SRP remains in contact with the SA and downstream sequences during further synthesis of approximately 30 amino acids. The contact with trigger factor is then restored unless another transmembrane segment reinitiates SRP binding. Importantly and in contrast to published data, the SRP appears perfectly capable of distinguishing SA sequences from signal sequences in secretory proteins at this early stage in biogenesis.
Department of Molecular Microbiology, Institute of Molecular Cell Biology, Vrije Universiteit, 1081 HV Amsterdam, The Netherlands.
Ronald S
RS
Ullers
Edith N G
EN
Houben
Josef
J
Brunner
Bauke
B
Oudega
Nellie
N
Harms
Joen
J
Luirink
D000595:Amino Acid Sequence; D003432:Cross-Linking Reagents / Q000737:chemistry; D003600:Cytosol / Q000378:metabolism; D000939:Epitopes / Q000737:chemistry; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins / Q000737:chemistry*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D019696:Peptidylprolyl Isomerase / Q000737:chemistry*; D010957:Plasmids / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism; D018271:Signal Recognition Particle / Q000737:chemistry*
D003432:Cross-Linking Reagents; D000939:Epitopes; D029968:Escherichia coli Proteins; D008565:Membrane Proteins; D010455:Peptides; D018271:Signal Recognition Particle; C403324:trigger factor, E coli; D019696:Peptidylprolyl Isomerase