A unique short signal sequence in membrane‐anchored proteins of Archaea

• Published in: Molecular microbiology Vol. 31; no. 5; pp. 1595 - 1596
• Main Authors: Albers, Sonja‐Verena, Konings, Wil N., Driessen, Arnold J. M.
• Format: Journal Article
• Language: English
• Published: Oxford BSL Blackwell Science Ltd 01.03.1999; Blackwell Publishing Ltd
• Subjects: Archaea - genetics; Carrier Proteins - genetics; Databases, Factual; Flagellin - metabolism; Glucose - metabolism; Membrane Proteins - genetics; Models, Biological; Molecular Sequence Data; Protein Processing, Post-Translational; Protein Sorting Signals - genetics; Sequence Homology, Amino Acid; Sulfolobus solfataricus
• DOI: 10.1046/j.1365-2958.1999.01286.x
• ISSN: 0950-382X

Detailed information is available on the signal sequences of bacteria and eukaryotes that direct secretory proteins out of the cell. It is generally assumed that such signals in Archaea are identical to the bacterial and eukaryotic signals. Recently, we have identified a glucose-binding protein in Sulfolobus solfataricus that functions as a subunit of an ABC type of sugar transporter. The binding protein is secreted by the cells in order to interact with the extracellular sugars. Unlike binding proteins in Gram-negative bacteria, the protein remains anchored to the membrane by means of an amino-terminal transmembrane segment. In this respect, it also differs from binding proteins of Gram-positive bacteria that use cysteine-linked lipid anchors for membrane binding. The determined N-terminal amino-acid sequence of the purified glucose binding protein completely matched the sequence predicted from the DNA sequence from the database of S. solfataricus, except that the first 12 predicted amino acids were lacking in the purified protein. The protein appears to be processed at a glycyl-leucyl peptide bond that precedes a putative transmembrane segment thought to anchor the secreted protein to the membrane. Although the program SIGNALP predicts an eukaryotic-type signal peptide cleavage site at amino acids 36-37 (Gly-Phe), a prokaryotic-type (Gram positive) signal peptide cleavage site at amino acids 43-44 (Pro-Ser), and a prokaryotic-type (Gram negative) one at amino acids 47-48 (Ala-Val), none of these sites are used. Cleavage at this position resembles strikingly that of the flagellins of methanogenic and halophilic Archaea. These secreted proteins bear a very short hydrophilic, positively charged N-terminal sequence of 11 or 12 amino acids (Fig. 1) that is processed at a glycine followed by a stretch of hydrophobic amino acids that seems to be involved in the intramolecular flagellin interactions.