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Another factor besides hydrophobicity can affect signal peptide interaction with signal recognition particle

S Matoba1, D M Ogrydziak

  • 1Institute of Marine Resources, University of California, Davis, California 95616, USA.

The Journal of Biological Chemistry
|July 21, 1998
PubMed

Insights

Yarrowia lipolytica alkaline extracellular protease (AEP) translocation to the endoplasmic reticulum depends on signal peptide properties beyond hydrophobicity. Signal peptide conformation influences the targeting pathway, affecting protein secretion efficiency.

Area of Science:

  • Molecular Biology
  • Protein Trafficking
  • Yeast Genetics

Background:

  • Protein translocation into the endoplasmic reticulum (ER) is crucial for secreted proteins in organisms like Yarrowia lipolytica.
  • The alkaline extracellular protease (AEP) in Y. lipolytica is translocated into the ER via a signal recognition particle (SRP)-dependent, cotranslational pathway.
  • A specific mutation, P17M, alters AEP translocation to an SRP-independent, posttranslational pathway.

Purpose of the Study:

  • To investigate the factors governing the switch between SRP-dependent and SRP-independent protein translocation pathways.
  • To identify mutations in the AEP signal peptide that alter its translocation mechanism.
  • To understand the role of signal peptide hydrophobicity and conformation in protein targeting to the ER.

Main Methods:

  • Site-directed mutagenesis was used to create mutations in the AEP signal peptide, including P17M and others.
  • Analysis of AEP precursor translocation kinetics and dependence on the signal recognition particle (SRP).
  • Computational modeling to assess the conformation and hydrophobicity of wild-type and mutant signal peptides.

Main Results:

  • Mutations were identified that restored SRP-dependent translocation of the P17M mutant AEP precursor.
  • Some mutations increased signal peptide hydrophobicity, but the A12P/P17M mutation restored SRP dependence without increasing hydrophobicity.
  • Signal peptide models suggest that 'kinked' conformations (wild-type, A12P/P17M) may favor SRP binding more than a 'straight' conformation (P17M).

Conclusions:

  • Signal peptide conformation, in addition to hydrophobicity, plays a critical role in determining the SRP-dependent or SRP-independent translocation pathway.
  • The findings suggest that the orientation of the signal peptide at the ribosomal surface influences SRP interaction and subsequent ER targeting.
  • These observations are particularly relevant for short, low-hydrophobicity signal peptides like that of AEP.

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