Cellular metabolism of proteins

Cellular system is capable of controlling metabolism of protein either by degrading protein or recycling amino acids back in to cell. For instance Proteasomes is proteolytic enzyme found attached to cellular system.

Proteasomes

Proteasomes are complex proteins that are found in most or all eukaryotes and archaea and some bacteria. They are very large and are dome shaped structure. Eukaryotic proteasomes are located in nucleus and cytoplasm. It helps in breaking of peptide bond by a proteolytic action with the help of enzymes called proteases. They help in cellular regulation of protein, thereby it degrades misfolded proteins. When a protein is proteolysed it yields amino acids of seven to eight in length. On further degradation it yields amino acids which helps in the synthesis of synthetic proteins.

Small proteins which are tagged for degradation of protein are referred as ubiquitin. Ubiquitin ligase is an enzyme that catalyzes the tagged protein. When an ubiquitin attaches to protein, this gives a signal for other ligases to attach the ubiquitin molecule.  As a result proteasomes bounds polyubiquitin chain. This polyubiquitin degrades tagged protein.

Proteasomes has central pore which are surrounded by core, i.e. four stacked rings. Of which two rings are present in interior of proteasomes and other two in outer surface. They look like large barrel structure. Every ring of proteasomes comprises seven proteins that are present as individual. Interior two rings consists of seven beta subunits includes six protease active moiety. Interior ring of proteasomes helps in target protein to enter the central core before it is degraded by proteins which are tagged. Outer two rings consist of seven alpha subunits. It acts as a gate in the entry point where protein enter the barrel structured proteasomes. Alpha subunits are bound to cap structure for effective controlling. By capping it act as a protein regulatory by distinguishing tagged polyubiquitin chain of protein substrates, thereby it starts degrading protein. Combination of ubiquitination and degradation of proteasomes is usually referred as ubiquitin proteasomes system. Proteasomes degradation metabolic pathway of protein plays a major role in cellular process. It helps in cell cycle, expressing gene regulated proteins and to control response to oxidative stress. This pathway discovery was awarded Nobel prize to Irwin Rose, Avram  herskho and Aaron Ciechanover in the year 2004.