Phospholamban, also known as PLN or PLB, is a
micropeptide
Micropeptides (also referred to as microproteins) are polypeptides with a length of less than 100-150 amino acids that are encoded by short open reading frames (sORFs). In this respect, they differ from many other active small polypeptides, which ...
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
that in humans is encoded by the ''PLN''
gene
In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
.
Phospholamban is a 52-
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...
integral membrane protein
An integral, or intrinsic, membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane. All ''transmembrane proteins'' are IMPs, but not all IMPs are transmembrane proteins. IMPs comprise a signi ...
that regulates the
calcium (Ca2+) pump in
cardiac muscle
Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle th ...
cells.
Function
This protein is found as a pentamer and is a major substrate for the cAMP-dependent protein kinase (
PKA) in cardiac muscle. In the unphosphorylated state, phospholamban is an inhibitor of cardiac muscle sarcoplasmic reticulum Ca
2+-ATPase (
SERCA2) which transports calcium from
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
into the
sarcoplasmic reticulum
The sarcoplasmic reticulum (SR) is a membrane-bound structure found within muscle cells that is similar to the smooth endoplasmic reticulum in other Cell (biology), cells. The main function of the SR is to store calcium ions (Ca2+). Calcium in bio ...
. When
phosphorylated
In chemistry, phosphorylation is the attachment of a phosphate group to a molecule or an ion. This process and its inverse, dephosphorylation, are common in biology and could be driven by natural selection. Text was copied from this source, wh ...
(by PKA) - disinhibition of Ca
2+-ATPase of SR leads to faster Ca
2+ uptake into the sarcoplasmic reticulum, thereby contributing to the
lusitropic response elicited in heart by
beta-agonists. The protein is a key regulator of
cardiac diastolic function. Mutations in this gene are a cause of inherited human
dilated cardiomyopathy
Dilated cardiomyopathy (DCM) is a condition in which the heart becomes enlarged and cannot pump blood effectively. Symptoms vary from none to feeling tired, leg swelling, and shortness of breath. It may also result in chest pain or fainting. Co ...
with refractory
congestive heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
.
When phospholamban is phosphorylated by PKA, its ability to inhibit SERCA2 is lost.
Thus, activators of PKA, such as the beta-adrenergic agonist
epinephrine
Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands and ...
(released by
sympathetic stimulation), may enhance the rate of cardiac myocyte relaxation. In addition, since SERCA2 is more active, the next
action potential
An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, ...
will cause an increased release of calcium, resulting in increased contraction (positive
inotropic
An inotrope is an agent that alters the force or energy of muscular contractions. Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction.
The term ''inotro ...
effect). When phospholamban is not phosphorylated, such as when PKA is inactive, it can interact with and inhibit SERCA. The overall effect of phospholamban is to decrease
contractility
Contractility refers to the ability for self-contraction, especially of the muscles or similar active biological tissue
*Contractile ring in cytokinesis
*Contractile vacuole
*Muscle contraction
**Myocardial contractility
*See contractile cell for ...
and the rate of
muscle relaxation
Muscle contraction is the activation of Tension (physics), tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscl ...
, thereby decreasing
stroke volume
In cardiovascular physiology, stroke volume (SV) is the volume of blood pumped from the left ventricle per beat. Stroke volume is calculated using measurements of ventricle volumes from an echocardiogram and subtracting the volume of the blood i ...
and
heart rate
Heart rate (or pulse rate) is the frequency of the heartbeat measured by the number of contractions (beats) of the heart per minute (bpm). The heart rate can vary according to the body's physical needs, including the need to absorb oxygen and excr ...
, respectively.
Clinical significance
Gene knockout
A gene knockout (abbreviation: KO) is a genetic technique in which one of an organism's genes is made inoperative ("knocked out" of the organism). However, KO can also refer to the gene that is knocked out or the organism that carries the gene kno ...
of phospholamban results in animals with
hyperdynamic hearts, with little apparent negative consequence.
Mutations in this gene are a cause of inherited human
dilated cardiomyopathy
Dilated cardiomyopathy (DCM) is a condition in which the heart becomes enlarged and cannot pump blood effectively. Symptoms vary from none to feeling tired, leg swelling, and shortness of breath. It may also result in chest pain or fainting. Co ...
with refractory
congestive heart failure
Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome, a group of signs and symptoms caused by an impairment of the heart's blood pumping function. Symptoms typically include shortness of breath, excessive fatigue, a ...
.
Discovery
Phospholamban was discovered by
Arnold Martin Katz Arnold Martin Katz (July 30, 1932 – January 25, 2016) was a medical doctor, professor of cardiology, medical researcher, and author of medical textbooks and research articles.
Career
Arnold Katz was born in Chicago, Illinois. His mother w ...
and coworkers in 1974.
Interactions
PLN has been shown to
interact
Advocates for Informed Choice, dba interACT or interACT Advocates for Intersex Youth, is a 501(c)(3) nonprofit organization using innovative strategies to advocate for the legal and human rights of children with intersex traits. The organizati ...
with
SLN and
SERCA1.
References
External links
PDBe-KB
provides an overview of all the structure information available in the PDB for Human Cardiac phospholamban
{{Calcium signaling
Protein domains
Single-pass transmembrane proteins