VAMP associated protein B and C
The VAPB gene provides instructions for making a protein that is found in cells throughout the body. Little is known about the function of the VAPB protein. Research indicates that this protein is associated with the membrane that surrounds the endoplasmic reticulum, a specialized structure within cells. Among its many functions, the endoplasmic reticulum folds newly formed proteins and prepares them for transport within the cell or to the cell surface. To function efficiently, the endoplasmic reticulum relies on a system that detects a buildup of unfolded or misfolded proteins. The cell's process for preventing or correcting a buildup of abnormal proteins is called the unfolded protein response. Researchers suggest that the VAPB protein plays an important role in the unfolded protein response.
Genetics Home Reference provides information about amyotrophic lateral sclerosis.
Researchers have identified one VAPB gene mutation in people with an adult-onset form of spinal muscular atrophy. This type of spinal muscular atrophy is characterized by muscle weakness and abnormal muscle movement that typically begin in early to mid-adulthood. The mutation that causes this condition replaces the amino acid proline with the amino acid serine at position 56 in the VAPB protein (written as Pro56Ser or P56S). The P56S mutation can cause amyotrophic lateral sclerosis (described above) in some people and spinal muscular atrophy in others. It is not known how the same mutation causes different conditions.
The abnormal VAPB protein cannot turn on (activate) the unfolded protein response. As a result, abnormal proteins form clumps (aggregates) in cells, resulting in cell death. Nerve cells that control muscle movement appear to be particularly vulnerable to cell death due to protein aggregates. The progressive loss of these nerve cells underlies the signs and symptoms of spinal muscular atrophy.
- VAMP (vesicle-associated membrane protein)-associated protein B and C