Single amino acid substitutions can convert the uncleaved signal-anchor of sucrase-isomaltase to a cleaved signal sequence.
A hydrophobic segment near the amino terminus (positions 12-32) of rabbit sucrase-isomaltase functions both as a membrane anchor and as a signal sequence for translocation into the endoplasmic reticulum. Unlike most signal sequences, that of sucrase-isomaltase is not cleaved by signal peptidase. Using in vitro transcription and translation systems, we have found that substitution of a single proline, at position 28 or 29, converted the signal-anchor to a cleaved signal sequence, with cleavage occurring after alanine 26 and the introduced proline thereby occupying position +2 or +3 relative to the cleavage site. Two deletions that shorten the transmembrane domain by 8 amino acids were also effective, whereas various other changes upstream and downstream of this domain were without effect. We conclude that susceptibility to mammalian signal peptidase is influenced both by the length of the hydrophobic region and by the secondary structure downstream of the cleavage site.
Hegner
M
M
Department of Biochemistry, Swiss Federal Institute of Technology, Zürich.
von Kieckebusch-Gück
A
A
Falchetto
R
R
James
P
P
Semenza
G
G
Mantei
N
N
D000595:Amino Acid Sequence; D000818:Animals; D003062:Codon; D004247:DNA / Q000235:genetics; D004285:Dogs; D008861:Microsomes / Q000378:metabolism; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010179:Pancreas / Q000378:metabolism; D010957:Plasmids; D014176:Protein Biosynthesis; D021382:Protein Sorting Signals / Q000235:genetics / Q000378:metabolism*; D011817:Rabbits; D013394:Sucrase-Isomaltase Complex / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D003062:Codon; D021382:Protein Sorting Signals; D004247:DNA; D013394:Sucrase-Isomaltase Complex