Signal recognition particle-dependent protein targeting, universal to all kingdoms of life |
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Authors: | H-G Koch M Moser and M Müller |
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Institution: | (1) Institut für Biochemie und Molekularbiologie, Universit?t Freiburg, Hermann-Herder-Stra?e 7, 79104, Freiburg, Germany, |
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Abstract: | The signal recognition particle (SRP) and its membrane-bound receptor represent a ubiquitous protein-targeting device utilized
by organisms as different as bacteria and humans, archaea and plants. The unifying concept of SRP-dependent protein targeting
is that SRP binds to signal sequences of newly synthesized proteins as they emerge from the ribosome. In eukaryotes this interaction
arrests or retards translation elongation until SRP targets the ribosome-nascent chain complexes via the SRP receptor to the
translocation channel. Such channels are present in the endoplasmic reticulum of eukaryotic cells, the thylakoids of chloroplasts,
or the plasma membrane of prokaryotes. The minimal functional unit of SRP consists of a signal sequence-recognizing protein
and a small RNA. The as yet most complex version is the mammalian SRP whose RNA, together with six proteinaceous subunits,
undergo an intricate assembly process. The preferential substrates of SRP possess especially hydrophobic signal sequences.
Interactions between SRP and its receptor, the ribosome, the signal sequence, and the target membrane are regulated by GTP
hydrolysis. SRP-dependent protein targeting in bacteria and chloroplasts slightly deviate from the canonical mechanism found
in eukaryotes. Pro- and eukaryotic cells harbour regulatory mechanisms to prevent a malfunction of the SRP pathway.
Electronic Publication |
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