CHM, Rab escort protein 1
The CHM gene provides instructions for producing the Rab escort protein-1 (REP-1), which is active (expressed) throughout the body. As an escort protein, REP-1 attaches (binds) to one of a number of Rab proteins. Following a chemical modification, REP-1 then directs the Rab protein to the membrane of one of the cell's compartments (organelles). While attached to the membrane, the Rab protein plays a role in directing the movement of proteins and organelles within cells (intracellular trafficking). After the Rab protein has reached its destination, it is released by REP-1 which then attaches to another Rab protein to begin the process again.
More than 140 mutations in the CHM gene have been found to cause choroideremia. Nearly all of these mutations lead to the production of an abnormally small, nonfunctional REP-1 protein. Other gene mutations result in a decrease in the protein's function or delete part or all of the gene and abolish REP-1 protein production. A lack of normal REP-1 disrupts the ability of Rab proteins to aid in intracellular trafficking. The immobility of proteins and organelles within the cell cause the cell to die prematurely.
The REP-1 protein is active (expressed) throughout the body, as is a similar protein, REP-2. Research suggests that when REP-1 is absent or not functioning properly, REP-2 can perform the protein escort duties of REP-1 in many of the body's tissues. Very little REP-2 protein is present in the light sensitive-tissue at the back of the eye (the retina), however, so it cannot compensate for the loss of REP-1 in this tissue. Loss of REP-1 function and subsequent misplacement of Rab proteins within the cells of the retina causes the progressive vision loss characteristic of choroideremia.
- choroideremia (Rab escort protein 1)
- REP-1, Rab escort protein 1
- Eurekah Bioscience Collection: Rab GTPases: Key Regulators of Membrane Trafficking
- Molecular Biology of the Cell (fourth edition, 2002): Membrane protein attachment by a fatty acid chain or a prenyl group
- Molecular Cell Biology (fourth edition, 2000): Covalently Attached Hydrocarbon Chains Anchor Some Proteins to the Membrane