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Coiled coil region of thrombospondin-4 (TSP-4) This family contains the N-terminal coiled coil region of TSP-4, which is abundantly expressed in tendon and muscle, as well as in neural and osteogenic tissues, and has also been detected in brain capillaries. It forms a pentameric left-handed coiled coil with a channel that is a unique carrier for lipophilic compounds. The pentamer is stabilized by inter-subunit disulfide bonds formed between cysteine residues adjacent to the C-terminal end of the coiled coil region. TSP-4 regulates the composition of the deposition of extracellular matrix (ECM) in tendon and skeletal muscle. The absence of TSP-4 alters the organization, composition and physiological functions of these tissues. TSP-4 deficiency causes incorrect modification of heparan-sulfate (HS), resulting in decreased activity of lipoprotein lipase (LpL) and loss of beta-glycan; HS is involved in a wide variety of cellular functions, LpL is an endothelial enzyme responsible for the uptake and hydrolysis of lipoproteins, and beta-glycan has inhibiting effect on TGF-beta signaling in skeletal muscle. The human gene THBS4 that encodes for TSP-4 contains a single nucleotide polymorphism (SNP), which is expressed at high frequency in Caucasians and associated with a significantly increased risk of premature myocardial infarction. TSP-4 also binds stromal interaction molecule 1 (STIM1), a transmembrane protein that functions in the endoplasmic reticulum (ER), and regulates calcium channel activity. Studies show that TSP-4 may act as an organizer of adhesive and axon outgrowth-promoting molecules in the ECM to optimize retinal ganglion cell responses. TSP-4 is also involved in the post-translational modification of collagen and may assist in collagen fibril assembly. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",