MYL7 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | MYL7 , MYL2A, MYLC2A, myosin light chain 7 | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 613993 MGI: 107495 HomoloGene: 23290 GeneCards: MYL7 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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Atrial Light Chain-2 (ALC-2) also known as Myosin regulatory light chain 2, atrial isoform (MLC2a) is a protein that in humans is encoded by the MYL7 gene. [5] [6] ALC-2 expression is restricted to cardiac muscle atria in healthy individuals, where it functions to modulate cardiac development and contractility. In human diseases, including hypertrophic cardiomyopathy, dilated cardiomyopathy, ischemic cardiomyopathy and others, ALC-2 expression is altered.
Human ALC-2 protein has a molecular weight of 19.4 kDa and is composed of 175 amino acids. [7] ALC-2 is an EF hand protein that binds to the neck region of alpha myosin heavy chain. [8] ALC-2 and the ventricular isoform, VLC-2, share 59% homology, showing significant differences at their N-termini and at the regulatory phosphorylation site(s), Serine-15 and Serine/Asparagine-14. [9]
ALC-2 expression has proven to be a useful marker of cardiac muscle chamber distinction, development and differentiation. [10] [11] [12] [13] [14] ALC-2 shows a pattern distinct from atrial essential light chain (ALC-1) during cardiogenesis. ALC-2 expression in adult murine hearts is cardiac-specific throughout embryonic days 8-16, and from day 12 and on is restricted to atria, showing very low levels in aorta and undetectable in ventricles, skeletal muscle, uterus, and liver. This atrial patterning occurs prior to septation. [15] Expression of ALC-2 has been shown to correlate with expression of alpha-myosin heavy chain in cardiac atria of non-human primates. [16]
ALC-2 and VLC-2 appear to function in the stabilization of thick filaments and regulation of contractility in the vertebrate heart. [17] Functional insights into ALC-2 function have come from studies employing transgenesis. A study in which the ventricular isoform of regulatory light chain was overexpressed to replace the ALC-2 in cardiac atria was performed. This substitution resulted in atrial myocytes that contract and relax more forcefully and quickly, resulting in atrial cardiomyocytes that behave as ventricular cardiomyocytes. [18]
In disease models, ALC-2 expression in some instances can be downregulated and replaced by the ventricular isoform (VLC-2). In spontaneously hypertensive rats, VLC-2 mRNA expression is three times higher in atria; and this change precedes any detectable pressure overloading of the heart, suggesting that this change is a very early functional adaptation to cardiac hypertrophy. [19] Moreover, in a porcine model of atrial fibrillation, VLC-2 mRNA expression showed the greatest change, being upregulated 9.4-fold and 7.3-fold in left and right atria, respectively. [20] In a porcine model of left atrial remodeling following mitral regurgitation, VLC-2 was shown to be upregulated. [21]
Human ALC-2 is phosphorylated at its N-terminus at Serine-15 by a cardiac-specific myosin light chain kinase; [22] [23] ALC-2 has a serine at position 14, which is an Asparagine in the ventricular isoform that is shown to be deamidated (thus producing a negative charge similar to phosphorylation). Whether serine-14 of human ALC-2 is also phosphorylated remains to be determined. Endogenous phosphorylation level is around 30% of the total ALC-2. [24] Alpha(1)-adrenergic stimulation by phenylephrine in atrial muscle strips showed an 80% increase in ALC-2 phosphorylation coordinate with enhanced contractile force, which was inhibited by both Rho kinase and myosin light chain kinase inhibition. [25] In a canine model of atrial fibrillation, decreased atrial contractility was associated with decreased ALC-2 and myosin binding protein C phosphorylation. [26] Moreover, the slow force response induced by stretch in human atrial muscle was shown to be modulated by enhanced phosphorylation of ALC-2 by myosin light chain kinase. [27]
Patients with hypertrophic cardiomyopathy shown an increased expression of ALC-2 in whole heart tissue. [28] In patients with mitral valve disease, ischemic cardiomyopathy, dilated cardiomyopathy, coronary heart disease and pressure overload-induced cardiac hypertrophy, ALC-2 was shown to be replaced with VLC-2 in cardiac atria; in dilated cardiomyopathy, this change was concomitant with enhanced sensitivity of atrial fibers to calcium. [29] [30]
In patients with congenital atrial septal defect carrying a missense mutation Ile820Asn in alpha myosin heavy chain, it was shown that binding of ALC-2 to alpha myosin heavy chain is disrupted. [31]
ALC-2 is shown to interact with:
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations. It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit muscle, the whole bundle or sheet of smooth muscle cells contracts as a syncytium.
MYH7 is a gene encoding a myosin heavy chain beta (MHC-β) isoform expressed primarily in the heart, but also in skeletal muscles. This isoform is distinct from the fast isoform of cardiac myosin heavy chain, MYH6, referred to as MHC-α. MHC-β is the major protein comprising the thick filament that forms the sarcomeres in cardiac muscle and plays a major role in cardiac muscle contraction.
Telokin is an abundant protein found in smooth-muscle. It is identical to the C-terminus of myosin light-chain kinase. Telokin may play a role in the stabilization of unphosphorylated smooth-muscle myosin filaments. Because of its origin as the C-terminal end of smooth muscle myosin light chain kinase, it is called "telokin".
Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates a specific myosin light chain, namely, the regulatory light chain of myosin II.
Myosin regulatory light polypeptide 9 is a protein that in humans is encoded by the MYL9 gene.
Protein kinase C epsilon type (PKCε) is an enzyme that in humans is encoded by the PRKCE gene. PKCε is an isoform of the large PKC family of protein kinases that play many roles in different tissues. In cardiac muscle cells, PKCε regulates muscle contraction through its actions at sarcomeric proteins, and PKCε modulates cardiac cell metabolism through its actions at mitochondria. PKCε is clinically significant in that it is a central player in cardioprotection against ischemic injury and in the development of cardiac hypertrophy.
Cardiac muscle troponin T (cTnT) is a protein that in humans is encoded by the TNNT2 gene. Cardiac TnT is the tropomyosin-binding subunit of the troponin complex, which is located on the thin filament of striated muscles and regulates muscle contraction in response to alterations in intracellular calcium ion concentration.
Tropomyosin alpha-1 chain is a protein that in humans is encoded by the TPM1 gene. This gene is a member of the tropomyosin (Tm) family of highly conserved, widely distributed actin-binding proteins involved in the contractile system of striated and smooth muscles and the cytoskeleton of non-muscle cells.
Myosin light-chain phosphatase, also called myosin phosphatase (EC 3.1.3.53; systematic name [myosin-light-chain]-phosphate phosphohydrolase), is an enzyme (specifically a serine/threonine-specific protein phosphatase) that dephosphorylates the regulatory light chain of myosin II:
A myosin light chain is a light chain of myosin. Myosin light chains were discovered by Chinese biochemist Cao Tianqin when he was a graduate student at the University of Cambridge in England.
ACTC1 encodes cardiac muscle alpha actin. This isoform differs from the alpha actin that is expressed in skeletal muscle, ACTA1. Alpha cardiac actin is the major protein of the thin filament in cardiac sarcomeres, which are responsible for muscle contraction and generation of force to support the pump function of the heart.
The myosin-binding protein C, cardiac-type is a protein that in humans is encoded by the MYBPC3 gene. This isoform is expressed exclusively in heart muscle during human and mouse development, and is distinct from those expressed in slow skeletal muscle (MYBPC1) and fast skeletal muscle (MYBPC2).
Troponin C, also known as TN-C or TnC, is a protein that resides in the troponin complex on actin thin filaments of striated muscle and is responsible for binding calcium to activate muscle contraction. Troponin C is encoded by the TNNC1 gene in humans for both cardiac and slow skeletal muscle. In slow skeletal muscle. structural analysis,anlaizie;10.164.138.220 Hotspot in for phone lunch everyday. Troponin C, also known as TN-C or TnC, is a protein that resides in the troponin complex on actin thin filaments of striated muscle and is responsible for binding
Myosin-10 also known as myosin heavy chain 10 or non-muscle myosin IIB (NM-IIB) is a protein that in humans is encoded by the MYH10 gene. Non-muscle myosins are expressed in a wide variety of tissues, but NM-IIB is the only non-muscle myosin II isoform expressed in cardiac muscle, where it localizes to adherens junctions within intercalated discs. NM-IIB is essential for normal development of cardiac muscle and for integrity of intercalated discs. Mutations in MYH10 have been identified in patients with left atrial enlargement.
Myosin regulatory light chain 2, ventricular/cardiac muscle isoform (MLC-2) also known as the regulatory light chain of myosin (RLC) is a protein that in humans is encoded by the MYL2 gene. This cardiac ventricular RLC isoform is distinct from that expressed in skeletal muscle (MYLPF), smooth muscle (MYL12B) and cardiac atrial muscle (MYL7).
Myosin heavy chain, α isoform (MHC-α) is a protein that in humans is encoded by the MYH6 gene. This isoform is distinct from the ventricular/slow myosin heavy chain isoform, MYH7, referred to as MHC-β. MHC-α isoform is expressed predominantly in human cardiac atria, exhibiting only minor expression in human cardiac ventricles. It is the major protein comprising the cardiac muscle thick filament, and functions in cardiac muscle contraction. Mutations in MYH6 have been associated with late-onset hypertrophic cardiomyopathy, atrial septal defects and sick sinus syndrome.
Myosin essential light chain (ELC), ventricular/cardiac isoform is a protein that in humans is encoded by the MYL3 gene. This cardiac ventricular/slow skeletal ELC isoform is distinct from that expressed in fast skeletal muscle (MYL1) and cardiac atrial muscle (MYL4). Ventricular ELC is part of the myosin molecule and is important in modulating cardiac muscle contraction.
Atrial Light Chain-1 (ALC-1), also known as Essential Light Chain, Atrial is a protein that in humans is encoded by the MYL4 gene. ALC-1 is expressed in fetal cardiac ventricular and fetal skeletal muscle, as well as fetal and adult cardiac atrial tissue. ALC-1 expression is reactivated in human ventricular myocardium in various cardiac muscle diseases, including hypertrophic cardiomyopathy, dilated cardiomyopathy, ischemic cardiomyopathy and congenital heart diseases.
Myosin light chain kinase, smooth muscle also known as kinase-related protein (KRP) or telokin is an enzyme that in humans is encoded by the MYLK gene.
Rho-associated protein kinase (ROCK) is a kinase belonging to the AGC family of serine-threonine specific protein kinases. It is involved mainly in regulating the shape and movement of cells by acting on the cytoskeleton.