Efficient function of signal peptidase 1 of Escherichia coli is partly determined by residues in the mature N-terminus of exported proteins

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Author(s)
Musik, Joanna E
Zalucki, Yaramah M
Day, Christopher J
Jennings, Michael P
Year published
2019
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Exported proteins require an N-terminal signal peptide to direct them from the cytoplasm to the periplasm. Once the protein has been translocated across the cytoplasmic membrane, the signal peptide is cleaved by a signal peptidase, allowing the remainder of the protein to fold into its mature state in the periplasm. Signal peptidase I (LepB) cleaves non-lipoproteins and recognises the sequence Ala-X-Ala. Amino acids present at the N-terminus of mature, exported proteins have been shown to affect the efficiency at which the protein is exported. Here we investigated a bias against aromatic amino acids at the second position ...
View more >Exported proteins require an N-terminal signal peptide to direct them from the cytoplasm to the periplasm. Once the protein has been translocated across the cytoplasmic membrane, the signal peptide is cleaved by a signal peptidase, allowing the remainder of the protein to fold into its mature state in the periplasm. Signal peptidase I (LepB) cleaves non-lipoproteins and recognises the sequence Ala-X-Ala. Amino acids present at the N-terminus of mature, exported proteins have been shown to affect the efficiency at which the protein is exported. Here we investigated a bias against aromatic amino acids at the second position in the mature protein (P2′). Maltose binding protein (MBP) was mutated to introduce aromatic amino acids (tryptophan, tyrosine and phenylalanine) at P2′. All mutants with aromatic amino acids at P2′ were exported less efficiently as indicated by a slight increase in precursor protein in vivo. Binding of LepB to peptides that encompass the MBP cleavage site were analysed using surface plasmon resonance. These studies showed peptides with an aromatic amino acid at P2′ had a slower off rate, due to a significantly higher binding affinity for LepB. These data are consistent with the accumulation of small amounts of preMBP in purified protein samples. Hence, the reason for the lack of aromatic amino acids at P2′ in E. coli is likely due to interference with efficient LepB activity. These data and previous bioinformatics strongly suggest that aromatic amino acids are not preferred at P2′ and this should be incorporated into signal peptide prediction algorithms.
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View more >Exported proteins require an N-terminal signal peptide to direct them from the cytoplasm to the periplasm. Once the protein has been translocated across the cytoplasmic membrane, the signal peptide is cleaved by a signal peptidase, allowing the remainder of the protein to fold into its mature state in the periplasm. Signal peptidase I (LepB) cleaves non-lipoproteins and recognises the sequence Ala-X-Ala. Amino acids present at the N-terminus of mature, exported proteins have been shown to affect the efficiency at which the protein is exported. Here we investigated a bias against aromatic amino acids at the second position in the mature protein (P2′). Maltose binding protein (MBP) was mutated to introduce aromatic amino acids (tryptophan, tyrosine and phenylalanine) at P2′. All mutants with aromatic amino acids at P2′ were exported less efficiently as indicated by a slight increase in precursor protein in vivo. Binding of LepB to peptides that encompass the MBP cleavage site were analysed using surface plasmon resonance. These studies showed peptides with an aromatic amino acid at P2′ had a slower off rate, due to a significantly higher binding affinity for LepB. These data are consistent with the accumulation of small amounts of preMBP in purified protein samples. Hence, the reason for the lack of aromatic amino acids at P2′ in E. coli is likely due to interference with efficient LepB activity. These data and previous bioinformatics strongly suggest that aromatic amino acids are not preferred at P2′ and this should be incorporated into signal peptide prediction algorithms.
View less >
Journal Title
Biochimica et Biophysica Acta - Biomembranes
Volume
1861
Issue
5
Copyright Statement
© 2019 Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence (http://creativecommons.org/licenses/by-nc-nd/4.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, providing that the work is properly cited.
Subject
Biochemistry and cell biology
Other biological sciences
Chemical engineering