PEVK repeats

Segment contains tandem Ig repeats and PEVK repeats, both acting as molecular spring elements. This segment is extensively differentially spliced. In the shortest cardiac-specific N2B titin isoform (linked to inclusion of exon 49), exon 50 is spliced direcdy to exon 225. In more compliant cardiac and skeletal titin isoforms, exon 50 is spliced to exon 51 (linked to additional inclusion of exons in the segment 52-224). 

Under the electron microscope titin appears as a flexible beaded string 4 nm in diameter. Most of the molecule is made up of repetitive domains of two types. In human cardiac titin there are 132 folded domains that resemble type III fibronectin repeats and 112 immunoglobulin-like domains.98 In a "PEVK region," between residues 163 and 2174, 70% of the residues are Pro, Glu, Val, or Lys. The titin molecule may be organized as polyproline helices in this elastic region.1023 At the C terminus of titin 800 residues, including a Ser / Thr protein kinase domain, are found within the M-line. 

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