Peroxisomes, protein targeting signals membrane proteins

Both the integral membrane proteins of peroxisomes as well as the peroxisomal matrix proteins are synthesised on free polyribosomes and are specifically targeted to peroxisomes via dedicated peroxisomal targeting signals. The biogenesis of peroxisomes follows a sequential pattern, which involves first the insertion of peroxisomal membrane proteins into the membrane of the pre-peroxisomal structure, derived from the endoplasmic reticulum, followed by insertion of the various matrix proteins. 

Proteins targeted to cytoplasmic compartments contain a variety of signaling sequences which direct them to the cytoplasmic face of membranes, mitochondria, the nucleus, or peroxisomes. 

The firefly enzyme might have its own problem by the fact that it is localized in vivo (yeast, mammalian, and plant cells as in the firefly lantern) in small vesicular structures called peroxisomes (55). This is due to the presence of a peroxisomal translocation signal located at the C-terminal domain of the molecule. The peroxisomal localization may present an additional membrane barrier for in situ detection of the enzyme, although it offers a particular advantage for studying protein transport or targeting to peroxisomes. Removal of the peroxisomal translocation signal has been shown to provide an alternative system in which the modified firefly luciferase is expressed as a cytoplasmic enzyme like bacterial luciferases. 

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