Signal peptide 501289 219704009 2008-06-16T14:20:59Z Gianlucaabate 7225096 /* Endoplasmic reticulum */ A '''signal peptide''' is a short (3-60 [[amino acid]]s long) [[peptide]] chain that directs the post-[[translation (genetics)|translational]] transport of a [[protein]]. Signal peptides may also be called '''targeting signals''', '''signal sequences''', '''transit peptides''', or '''localization signals'''. The amino acid sequences of signal peptides direct proteins (which are synthesized in the [[cytosol]]) to certain [[organelle]]s such as the [[Cell nucleus|nucleus]], [[mitochondrial matrix]], [[endoplasmic reticulum]], [[chloroplast]], [[apoplast]] and [[peroxisome]]. Some signal peptides are cleaved from the protein by ''signal [[peptidase]]'' after the proteins are transported. == Types by protein destination == === Endoplasmic reticulum === Almost all proteins that are transported to the [[endoplasmic reticulum]] have a sequence consisting of 5-10 hydrophobic amino acids on the [[N-terminal end|N-terminus]]. The protein is guided to the ER by a [[signal-recognition particle]] (SRP), which moves between the ER and the cytoplasm. It binds to the signal peptide. The SRP binds to the signal peptide as soon as it is synthesised and extruded from the ribosome. This causes a pause in protein synthesis, most probably allowing the ribosome-SRP complex time to bind to the SRP receptor on the target ER membrane. The SRP protein is thought to be a regulatory GTP protein. Conformational changes may therefore lead to the SRP release. The protein may then be threaded through the ER membrane by a translocator pore. Most of these proteins are transported from the endoplasmic reticulum to the [[Golgi apparatus]]. If these proteins have a particular 4-amino-acids sequence on the [[C-terminal end|C-terminus]], these proteins stay in the endoplasmic reticulum. === Nucleus === {{main|nuclear localization signal}} A ''[[nuclear localization signal]]'' (NLS) is a signal peptide directing to the nucleus and is often a unit consisting of plus-charged amino acids. The NLS normally is located inside the peptide chain. === Nucleolus === The [[nucleolus]] within the nucleus can be targeted with a sequence called a ''nucleolar localization signal'' (abbreviated NoLS or NOS). === Mitochondrial matrix === The signal peptide that directs to the mitochondrial [[Matrix (biology)|matrix]] has a sequence consisting of an alternating pattern with a few hydrophobic amino acids and a few plus-charged amino acids form. It is usually called the ''mitochondrial targeting signal'' (MTS). === Peroxisome === There are two types of signal peptides directing to peroxisome, which are called ''[[peroxisomal targeting signal]]s'' (PTS). One is PTS1, which is made of three amino acids on the C-terminus. The other is PTS2, which is made of a 9-amino-acid sequence often present on the N-terminus of the protein. ==Types== Following is a list of types of signal peptides: *N-terminus signal peptides often target the [[mitochondrial matrix]], [[endoplasmic reticulum]] and [[peroxisome]]. *C-terminus signal peptides often target the [[peroxisome]]. ==Examples of signal peptides== Transport to the [[Cell nucleus|nucleus]] (NLS) -Pro-Pro-Lys-Lys-Lys-Arg-Lys-Val- &nbsp; Transport to the [[endoplasmic reticulum]] H<sub>2</sub>N-Met-Met-Ser-Phe-Val-Ser-Leu- Leu-Leu-Val-Gly-Ile-Leu-Phe- Trp-Ala-Thr-Glu-Ala-Glu-Gln- Leu-Thr-Lys-Cys-Glu-Val-Phe- Gln- &nbsp; Retention to the [[endoplasmic reticulum]] -Lys-Asp-Glu-Leu-COOH &nbsp; Transport to the [[mitochondrial matrix]] H<sub>2</sub>N-Met-Leu-Ser-Leu-Arg-Gln-Ser- Ile-Arg-Phe-Phe-Lys-Pro-Ala- Thr-Arg-Thr-Leu-Cys-Ser-Ser- Arg-Tyr-Leu-Leu- &nbsp; Transport to the [[peroxisome]] (PTS1) -Ser-Lys-Leu-COOH &nbsp; Transport to the [[peroxisome]] (PTS2) H<sub>2</sub>N-----Arg-Leu-X<sub>5</sub>-His-Leu- &nbsp; H<sub>2</sub>N is the N-terminus of a protein. COOH is the C-Terminus of a protein. ==See also== * [[Protein targeting]] ==External links== * {{MeshName|Signal+Peptide}} * [http://proline.bic.nus.edu.sg/spdb/ SPdb (Signal Peptide DataBase)] [[Category:Gene expression]] [[Category:Protein targeting]] [[de:Signalsequenz]] [[fr:Peptide signal]] [[ja:シグナルペプチド]] [[lt:Lyderinė seka]] [[pl:Sekwencja sygnałowa]] [[ru:Сигнальный пептид]]