The ribosome-bound Hsp70 homolog Ssb of Saccharomyces cerevisiae.
The Hsp70 homolog Ssb directly binds to the ribosome and contacts a variety of newly synthesized polypeptide chains as soon as they emerge from the ribosomal exit tunnel. For this reason a general role of Ssb in the de novo folding of newly synthesized proteins is highly suggestive. However, for more than a decade client proteins which require Ssb for proper folding have remained elusive. It was therefore speculated that Ssb, despite its ability to interact with a large variety of nascent polypeptides, may assist the folding of only a small and specific subset. Alternatively, it has been suggested that Ssb's function may be limited to the protection of nascent polypeptides from aggregation until downstream chaperones take over and actively fold their substrates. There is also evidence that Ssb, in parallel to a classical chaperone function, is involved in the regulation of cellular signaling processes. Here we aim to summarize what is currently known about Ssb's multiple functions and what remains to be ascertained by future research.
Department of Cell and Molecular Biology, Biomedicinskt Centrum BMC, Uppsala, Sweden.
Kristin
K
Peisker
Marco
M
Chiabudini
Sabine
S
Rospert
D000595:Amino Acid Sequence; D003600:Cytosol / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D008954:Models, Biological; D018832:Molecular Chaperones / Q000737:chemistry; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D012270:Ribosomes / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014158:Transcription, Genetic
D018840:HSP70 Heat-Shock Proteins; D018832:Molecular Chaperones; D010455:Peptides; C095192:SSB1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins