Group of Biochemistry

Life of proteins and cellular functions

Proteins are major key players in living systems; their amino-acid sequences are controlled by the genetic information in DNA.  Newly synthesized proteins need to fold into their native conformations in order to become functional.  However, recent evidence shows that this process is not spontaneous, but instead requires helper proteins called molecular chaperones.

Translocators controlling mitochondrial protein import.

Eukaryotic cells contain several membrane-bound compartments or organelles. By virtue of this compartmentalization, they can perform complex reactions in parallel in distinct compartments, and store energy by distributing substances asymmetrically to the organellar membranes.  To perform their functions, organelles need to place resident proteins in correct intraorganellar locations.   To this end, cells employ protein translocators in the organellar membranes as well as soluble molecular chaperones. Together, these factors control the protein traffic and deliver newly synthesized proteins to the appropriate destination compartments.  The protein translocators are protein nano-machines that perform multiple tasks: they function as receptors for targeting signals; provide a protein-conducting channel through which newly synthesized proteins cross the organellar membrane in an unfolded state; and generate a driving force to achieve vectorial movement of the translocating polypeptide chain.  Much recent interest has been focused on how the translocators perform these complex functions correctly and efficiently.
Even after folding into their native structures in the appropriate destination compartments, some proteins may become nonfunctional due to stresses placed on cells, such as high temperature, exposure to heavy metals, and oxidative stresses.  In these cases, various types of molecular chaperones are utilized to repair the aberrant proteins.  If efforts to renature proteins fail, the aberrant proteins are subjected to disposal by degradation systems.  Central questions remaining to be answered include how the cell discriminates between normal and aberrant proteins, and how the final judgment on protein fate is made.   It also remains unknown whether protein quality control has profound biological significance in multicellular organisms, in processes such as fertilization and development of higher plants.

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