Lamin
Encyclopedia
Nuclear lamins, also known as Class V intermediate filaments, are fibrous protein
s providing structural function and transcriptional regulation in the cell nucleus
. Nuclear lamins interact with membrane-associated proteins to form the nuclear lamina
on the interior of the nuclear envelope. They are involved in the breakdown and reformation of the nuclear envelope during mitosis
, as well as the positioning of nuclear pores.
cells, there are A- and B-type lamins, which differ in their length and pI
. Human cells have three differentially regulated gene
s.
, the nuclear lamina
-- a proteinaceous structure layer subjacent to the inner surface of the nuclear envelope
and throughout the nucleoplasm in the nucleoplasmic "veil".
Comparison of the lamins to cytoskeletal intermediate filaments shows that lamins have an extra 42 residues (six heptads) within coil 1b. The c-terminal tail domain contains a nuclear localization signal
(NLS), an Ig-fold-like domain, and in most cases a'][;p carboxy-terminal CaaX box that is isoprenylated and carboxymethylated (lamin C does not have a CAAX box). Lamin A is further processed to remove the last 15 amino acids and its farnesylated cysteine.
Lamin A and lamin C form homodimers which associate head to tail.
During mitosis, lamins are phosphorylated by Mitosis-Promoting Factor (MPF), which drives the disassembly of the lamina and the nuclear envelope. After chromosome segregation, dephosphorylation of nuclear lamins promotes reassembly of the nuclear envelope.
Fibrous protein
Scleroproteins, or fibrous proteins, constitute one of the three main classes of proteins, alongside globular proteins and conjugated proteins.Keratin, collagen, elastin, and fibroin are all scleroproteins...
s providing structural function and transcriptional regulation in the cell nucleus
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
. Nuclear lamins interact with membrane-associated proteins to form the nuclear lamina
Nuclear lamina
The nuclear lamina is a dense fibrillar network inside the nucleus of a eukaryotic cell. It is composed of intermediate filaments and membrane associated proteins. Besides providing mechanical support, the nuclear lamina regulates important cellular events such as DNA replication and cell division...
on the interior of the nuclear envelope. They are involved in the breakdown and reformation of the nuclear envelope during mitosis
Mitosis
Mitosis is the process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets, in two separate nuclei. It is generally followed immediately by cytokinesis, which divides the nuclei, cytoplasm, organelles and cell membrane into two cells containing roughly...
, as well as the positioning of nuclear pores.
A, B, and C types
In animalAnimal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
cells, there are A- and B-type lamins, which differ in their length and pI
Isoelectric point
The isoelectric point , sometimes abbreviated to IEP, is the pH at which a particular molecule or surface carries no net electrical charge....
. Human cells have three differentially regulated gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
s.
- B-type lamins are present in every cell. B type lamins, B1 and B2, are expressed from the LMNB1LMNB1Lamin-B1 is a protein that in humans is encoded by the LMNB1 gene.-Interactions:LMNB1 has been shown to interact with Thymopoietin.-Further reading:...
and LMNB2 genes on 5q23 and 19q13, respectively. - A-type lamins are expressed only following gastrulationGastrulationGastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar structure known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm.Gastrulation takes place after cleavage...
. Lamin A and C are the most common A-type lamins and are splice variants of the LMNALMNALamin A/C also known as LMNA is a protein that in humans is encoded by the LMNA gene. Lamin A/C belongs to the lamin family of proteins.-Function:...
gene found at 1q21. - C-type lamins are also subject to tissue-specific expression.
Function and structure
These proteins localize to two regions of the nuclear compartmentCell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, the nuclear lamina
Nuclear lamina
The nuclear lamina is a dense fibrillar network inside the nucleus of a eukaryotic cell. It is composed of intermediate filaments and membrane associated proteins. Besides providing mechanical support, the nuclear lamina regulates important cellular events such as DNA replication and cell division...
-- a proteinaceous structure layer subjacent to the inner surface of the nuclear envelope
Nuclear envelope
A nuclear envelope is a double lipid bilayer that encloses the genetic material in eukaryotic cells. The nuclear envelope also serves as the physical barrier, separating the contents of the nucleus from the cytosol...
and throughout the nucleoplasm in the nucleoplasmic "veil".
Comparison of the lamins to cytoskeletal intermediate filaments shows that lamins have an extra 42 residues (six heptads) within coil 1b. The c-terminal tail domain contains a nuclear localization signal
Nuclear localization signal
A nuclear localization signal or sequence is an amino acid sequence which 'tags' a protein for import into the cell nucleus by nuclear transport. Typically, this signal consists of one or more short sequences of positively charged lysines or arginines exposed on the protein surface. Different...
(NLS), an Ig-fold-like domain, and in most cases a'][;p carboxy-terminal CaaX box that is isoprenylated and carboxymethylated (lamin C does not have a CAAX box). Lamin A is further processed to remove the last 15 amino acids and its farnesylated cysteine.
Lamin A and lamin C form homodimers which associate head to tail.
During mitosis, lamins are phosphorylated by Mitosis-Promoting Factor (MPF), which drives the disassembly of the lamina and the nuclear envelope. After chromosome segregation, dephosphorylation of nuclear lamins promotes reassembly of the nuclear envelope.