Proteins have to reach right destination in the organism or within the cell to correctly accomplish their functions.As protein is translated,the peptide chain may expose to a variety of highly specific sequence signals.
One such signal is "ZIP code" which is used by the cell to direct the protein to the appropriate compartment (in or out of the cell).This process always involves the transport of the protein across one or several membranes & is also referred to as translocation.The activity or destination of a protein-
- getting attached to the cell membrane,
- being secreted outside the cell,
- being transported into the periplasm (incase of bacteria),
- being transported to the mitochondria or any other organelle,
- being transported into the cell nucleus.
A newly synthesized peptide chain is converted into a functional protein by the folding of this chain into a compact & stable 3-D structure.The final structure of a protein generally consists of several relative independent domains.
Most natural proteins are made of combination of 1 to 10 domains picked from a set of a few thousands.The domains are identifiable by their scaffold sequence signatures (the motif in the protein means amino acid texts that remain recognisable despite a zillion years of divergent evolution).The domain architecture underlying a particular protein sequence provides hints about the possible 3-D structure of it & its potential biochemical or cellular functions.
The recognition & definition of protein domains is a major research topic of Bio-informatics.