Fibronectin connecting sequence

The carboxy-terminal region in apolipoprotein (a) closely resembles the protease domain in plasminogen [eight amino acid substitutions, nine amino acid deletions, and one insertion in apo(a) relative to plasminogen, with 94% overall nucleotide sequence identity] (G28). The most important difference is the substitution of arginine by serine in the site responsible for proteolytic activity (position 4308) (G28). As a result, Lp(a) has no protease activity towards substrates for plasmin (J3). Salonen (SI) reported a serine-protease activity of Lp(a) towards fibronectin, a glycoprotein present in connective tissue matrices. 

Komoriya, A., Green, L. J., Mervic, M., et al. The minimal essential sequence for a major cell type-specific adhesion site (CS1) within the alternatively spliced type III connecting segment domain of fibronectin is leucine-aspartic acid-valine. J. Biol. Chem. 266 15075-15079, 1991. 

On such modified surfaces, some of the attached proteins are recognized by cytoskeletally associated receptors in the cell membrane. So, in the end, the extracellular substrate is mechanically connected with the intracellular cytoskele-ton, which may secrete its own adhesion proteins. Integrins, as an important class of cell receptors [63], bind to small domains on their adhesion proteins, e.g., the oligopeptide sequence arginine-glycine-aspartic acid (RGD) that is common in fibronectin [64],... 

Fibronectin is an adhesion protein like laminin, vitronectin, and von Wille-brand factor, which are synthesized by the cells themselves to build up the ECM. The glycoprotein fibronectin with a molecular weight between 220,000 and 250,000 consists of two similar subunits, which are connected close to their C-terminus by disulfide bridges. The subunits are composed of functional domains [121]. The cell binding domain with the characteristic sequence Gly-Arg-Gly-Asp-Ser (GRGDS) is of special interest [122]. Models of the subunit of the fibronectin molecule and its cell binding domain are presented in Fig. 21. 

Mardilovich and KokkoU postulated that, for a small peptide to effectively mimic the ttjPj binding site of fibronectin, the primary (RGD) and synergistic (PHSRN) binding sequences must be connected by a linker that approximates both the distance and hydrophobicity/hydrophilicity between the fibronectin sequences, which results in a neutral linker (Mardilovich and Kokkoli, 2004). 

Historically, these peptides were identified by isolating domains ofinterest from naturally evolved proteins. The tripeptide RGD sequence (arginine-glycine—aspartic acid), a commonly used cell-adhesion domain, is a prime example of this. RGD was isolated in 1983 from the extracellular and plasma protein fibronectin and was identified as the minimal sequence necessary to promote cell-attachment properties (Pierschbacher and Ruoslahti 1984). Other commonly used domains include elastin-hke sequences, which are derived from the protein elastin found in connective tissue (Meyer and Chilkoti 2002), and recombinant-silks (Prince et al. 1995). Both of these peptide domains are used to confer their unique mechanical properties (i.e., resilience, elasticity, and strength) to the resulting biomaterial. 

---