Kringle motifs

CHAPTER 36, FIGURE 5 Motif structures within coagulation proteins. Common motifs are found in the amino terminal regions of the proteinase precursor molecules. Shown are the kringle motifs and EGF-like motifs found in the vitamin K-dependent proteins and in plasminogen. Fibronectin (types I and II) motifs and apple motifs (named from their two-dimensional representations) are also present but not shown. Some epidermal growth factor-like domains contain P-hydroxylated Asp residues. The cartoon structures for the motifs are derived from three-dimensional structures determined by x-ray crystallography or by two-dimensional NMR spectroscopy. 

The heterogeneity of Lp(a) is related to ultrastructural motifs in the molecule, strongly resembling the so-called kringles found in both plasminogen and other plasma proteins, such as proteases of the coagulation system (tissue type plasminogen activator and prothrombin) (Fig. 2). 

The four common motifs found within the amino terminal regions of the proteinase precursors and proteinases are kringles, epidermal growth factor (EGF)-like motifs, fibronectin motifs, and apple motifs (Figure 36-5). The kringle is so named because in two dimensions, i.e., on paper prior to determination of its three-dimensional structure, it has the shape of a Danish pretzel. Similarly, apple motifs resemble drawings of apples. 

A structural domain consists of 100-150 residues in various combinations of motifs. Often a domain is characterized by some interesting structural feature an unusual abundance of a particular amino acid (e.g., a prollne-rich domain, an acidic domain), sequences common to (conserved in) many proteins (e.g., SH3, or Src homology region 3), or a particular secondary-structure motif (e.g., zinc-finger motif in the kringle domain). 

---