The code for directing proteins for translocation across ER membrane

SRP cotranslationally recognizes specific features of a signal sequence

Ingmarie Nilsson, Patricia Lara, Tara Hessa, Arthur E. Johnson, Gunnar Von Heijne, Andrey L. Karamyshev

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

The signal recognition particle (SRP) cotranslationally recognizes signal sequences of secretory proteins and targets ribosome-nascent chain complexes to the SRP receptor in the endoplasmic reticulum membrane, initiating translocation of the nascent chain through the Sec61 translocon. Although signal sequences do not have homology, they have similar structural regions: a positively charged N-terminus, a hydrophobic core and a more polar C-terminal region that contains the cleavage site for the signal peptidase. Here, we have used site-specific photocrosslinking to study SRP-signal sequence interactions. A photoreactive probe was incorporated into the middle of wild-type or mutated signal sequences of the secretory protein preprolactin by in vitro translation of mRNAs containing an amber-stop codon in the signal peptide in the presence of the Nε-(5-azido-2 nitrobenzoyl)-Lys-tRNAamb amber suppressor. A homogeneous population of SRP-ribosome-nascent chain complexes was obtained by the use of truncated mRNAs in translations performed in the presence of purified canine SRP. Quantitative analysis of the photoadducts revealed that charged residues at the N-terminus of the signal sequence or in the early part of the mature protein have only a mild effect on the SRP-signal sequence association. However, deletions of amino acid residues in the hydrophobic portion of the signal sequence severely affect SRP binding. The photocrosslinking data correlate with targeting efficiency and translocation across the membrane. Thus, the hydrophobic core of the signal sequence is primarily responsible for its recognition and binding by SRP, while positive charges fine-tune the SRP-signal sequence affinity and targeting to the translocon.

Original languageEnglish (US)
Pages (from-to)1191-1201
Number of pages11
JournalJournal of Molecular Biology
Volume427
Issue number6
DOIs
StatePublished - Mar 27 2015

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Signal Recognition Particle
Protein Transport
Protein Sorting Signals
Membranes
Protein Biosynthesis
Ribosomes
Proteins
Terminator Codon
Endoplasmic Reticulum
Canidae

Keywords

  • photocrosslinking
  • protein targeting
  • protein translocation
  • signal sequence
  • SRP

ASJC Scopus subject areas

  • Molecular Biology

Cite this

The code for directing proteins for translocation across ER membrane : SRP cotranslationally recognizes specific features of a signal sequence. / Nilsson, Ingmarie; Lara, Patricia; Hessa, Tara; Johnson, Arthur E.; Von Heijne, Gunnar; Karamyshev, Andrey L.

In: Journal of Molecular Biology, Vol. 427, No. 6, 27.03.2015, p. 1191-1201.

Research output: Contribution to journalArticle

Nilsson, Ingmarie ; Lara, Patricia ; Hessa, Tara ; Johnson, Arthur E. ; Von Heijne, Gunnar ; Karamyshev, Andrey L. / The code for directing proteins for translocation across ER membrane : SRP cotranslationally recognizes specific features of a signal sequence. In: Journal of Molecular Biology. 2015 ; Vol. 427, No. 6. pp. 1191-1201.
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