Fibromodulin is a
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, respon ...
that in humans is encoded by the ''FMOD''
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 b ...
.
Fibromodulin is a 42kDa
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, respon ...
of a family of small interstitial leucine-rich repeat
proteoglycans (SLRPs). It can have up to four N-linked
keratan sulfate chains attached to the core protein within the leucine-rich region. It shares significant
sequence homology with
biglycan and
decorin.
Function
Fibromodulin participates in the assembly of the collagen fibers of the extracellular matrix. It binds to the same site on the
collagen type I molecule as
lumican. It also inhibits fibrillogenesis of
collagen type I and collagen type III ''in vitro''.
It regulates TGF-beta activities by sequestering TGF-beta into the extracellular matrix.
Clinical significance
There is an age-dependent decline in the synthesis of
keratan sulfate chains, so non-glycated forms of fibromodulin can accumulate in tissues such as
cartilage.
Fibromodulin is found in the
epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the ...
of human
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
and is expressed by skin cells (
keratinocyte
Keratinocytes are the primary type of cell found in the epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells.
Basal cells in the basal layer (''stratum basale'') of the skin are sometimes referred ...
s) in culture. Mice with the gene for fibromodulin knocked out (Fmod-/-) have very fragile
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
and abnormal tail and
Achilles tendons.
The
collagen fiber bundles in these tendons are fewer and disorganised and there is less endotenon surrounding the tendon tissue. The levels of
lumican, a SLRP with one of the same collagen binding sites as fibromodulin, is increased 4 fold in the tail tendons of Fmod-knockout mice.
References
Further reading
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Extracellular matrix proteins
Glycoproteins
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