Trypsin myosin fragmentation

When myosin is digested with trypsin, two myosin fragments (meromyosins) are generated. L ht mero-myosin (LMM) consists of aggregated, insoluble a-he-hcal fibers from the tail of myosin (Figure 49 ). LMM... 

Figure 14.15 Stmcture of the SI fragment of chicken myosin as a Richardson diagram (a) and a space-filling model (b). The two light chains are shown in magenta and yellow. The heavy chain is colored according to three proteolytic fragments produced by trypsin a 25-kDa N-terminal domain (green) a central 50-kDa fragment (red) divided by a cleft into a 50K upper and a 50K lower domain and a 20-kDa C-terminal domain (blue) that links the myosin head to the coiled-coil tail. The 50-kDa and 20-kDa domains both bind actin, while the 25-kDa domain binds ATP. [(b) Courtesy of 1. Rayment.]...

Figure 4.5. Structure of myosin. Myosin comprises both light and heavy chains. The heavy chains may be cleaved by trypsin to generate light meromyosin (LMM) and heavy mero-myosin (HMM). Papain digestion of HMM yields subfragments SI and S2 each SI fragment contains an ATPase site and an actin-binding site. The light chains modify the activity of the ATPase.

S ATP -I- myosin I heavy chain <1, 2, 9-11> (<10> major site of phosphorylation is Ser8 [22] <2> 35 kDa trypsin fragment of the C-terminus of the maximally activated, phosphorylated enzyme is fully catalytically active and contains 2 thirds of the autophosphorylation sites of the native enzyme [20] <9,10> substrate myosin ID [19,22] <2> higher activity with membrane-bound substrate myosin I [17] <2> substrates are heavy chains of myosin lA and IB [6,7,17] <2,11> substrate is heavy chain of myosin IC [7,23,24] <2> a basic amino acid is essential on amino-terminal side of phosphorylation site, two are preferable, and a Tyr-residue is essential two residues away on the COOH-terminal side [7] <2> contains two myosin heavy chain kinases one for myosin I and one for myosin II... 

Cleavage of the -850-residue SI heads with trypsin yields mainly three large fragments that correspond to structural domains of the intact protein as shown in Fig. 19-15. They are known as the 25-kDa (N-terminal), 50-kDa, and 20-kDa fragments, and for myosin from D. discoideum correspond to residues 1 to 204,216 to 626, and 647 to 843, respectively. The ATP-binding site is in a deep cleft between the 20-kDa and 50-kDa... 

Figure 8.10 Schematic drawing of the myosin molecule. Note that trypsin produces two fragments, light and heavy meromyosins.

Let us first consider the structure of myosin. The results of electron microscopic studies of skeletal-muscle myosin show it to be a two-headed structure linked to a long stalk (Figure 34.2). As we saw in Chapter 33, limited proteolysis can be a powerful tool in probing the activity of large proteins. The treatment of myosin with trypsin and papain results in the formation of four fragments two SI fragments an S2 fragment, also called heavy... 

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