Transit signal peptide

The inner envelope membrane proteins have a cleavable N-terminal transit peptide, as well as some hydrophobic domain (s) in their mature portion. There are two possibilities on the role of this hydrophobic domain it may work as an N-terminal signal peptide after the translocation into the stroma and the subsequent cleavage of the transit peptide. Alternatively, it may work as a stop-transfer signal. One more important question is how the distinction is made between the outer membrane proteins, the inner membrane proteins, and the thylakoid membrane proteins. It is still an enigma. 

ER and periplasm targeting signal peptide ------1 BGB-domain with blue copper binding site TP - Transit Peptide... 

I Signal peptide I Transit peptide L l i.iI AGP-like domain... 

Target (htq) //www.cbs.dtu.dk/servicesA argetP/) assigns the subcellular location of proteins based on the predictions of the N-terminal chloroplast transit peptide, mitochondrial targeting peptide or secretory signal peptide. 

SIGNAL from sig peptide TRANSIT from transit peptide CHAIN from mat peptide... 

Although the chloroplast transit peptide has been studied relatively thoroughly, further intrachloroplastic sorting signals have not been well understood. Some of them are introduced below in the context of describing the known sorting pathways (Keegstra and Cline, 1999 Chen and Schnell, 1999 Cline and Henry, 1996 Kouranov and Schnell, 1996). 

However, there is another class of outer membrane proteins (such as Toc34) that do not have a cleavable transit peptide. These proteins appear to be relatively small. A study suggested that their signal resides on the N-terminal 30 residues (Li and Chen, 1996). The signal consists of a positively charged N-terminal portion followed by a hydrophobic core, although it is not certain whether this feature is general. 

Import into the endoplasmic reticulum requires an N-terminal signal sequence that contains a long stretch of hydrophobic amino acids. The mitochondrial transit peptide is a hydrophilic sequence rich in serine and threonine, with regularly spaced basic amino acids. Import into the ER requires the signal recognition particle and its receptor, but mitochondrial import does not require the SRP and presumably uses a different receptor. Import into mitochondria requires a membrane potential, but import into the ER does not. 

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