Phospholamban
Phospholamban (PLN) is a small protein that plays a crucial role in cardiac muscle contraction and relaxation. It is primarily found in the sarcoplasmic reticulum (SR), a specialized type of endoplasmic reticulum in muscle cells.
Structure[edit | edit source]
Phospholamban is a pentameric protein, meaning it is composed of five identical subunits. Each subunit consists of 52 amino acids and has a molecular weight of approximately 6 kDa. The protein has both hydrophilic and hydrophobic regions, allowing it to interact with both the aqueous environment of the cell and the lipid bilayer of the SR membrane.
Function[edit | edit source]
Phospholamban regulates the activity of the sarcoplasmic reticulum calcium ATPase (SERCA), an enzyme that pumps calcium ions (Ca2+) from the cytosol of the cell into the SR. By inhibiting SERCA, phospholamban decreases the rate of Ca2+ uptake into the SR, thereby slowing the relaxation of the cardiac muscle after contraction.
When phospholamban is phosphorylated by protein kinase A (PKA) or calcium/calmodulin-dependent protein kinase II (CaMKII), it releases its inhibition on SERCA, allowing for faster Ca2+ uptake and quicker muscle relaxation. This phosphorylation is a key part of the fight-or-flight response, as it allows the heart to beat faster and stronger in response to stress.
Clinical significance[edit | edit source]
Mutations in the gene encoding phospholamban can lead to various forms of cardiomyopathy, a disease of the heart muscle. For example, a mutation that prevents phospholamban from being properly phosphorylated can lead to dilated cardiomyopathy, a condition in which the heart becomes enlarged and cannot pump blood efficiently.
See also[edit | edit source]
- Cardiac muscle
- Sarcoplasmic reticulum
- Sarcoplasmic reticulum calcium ATPase
- Protein kinase A
- Calcium/calmodulin-dependent protein kinase II
- Cardiomyopathy
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