Myosin S1

PDB file 1B7T

This file depicts the S1 head of scallop myosin complexed with Mg⁺⁺-ADP.  The structure was solved by A. Houdusse, V. Kalabokis, D. Himmel, A.G. Szent-Gyorgyi, & C. Cohen in 1999. The authors interpret the conformation of the myosin head as representing a pre-hydrolysis (ATP) state of the contractile cycle in which the myosin head is detached from actin.

Suggested display options:

Color the protein chain and display as cartoon.
Select hetero-ligand, display as spacefill, and color CPK. 

Note how each light chain wraps around the a-helix of the heavy chain. Compare if possible to the structure of calmodulin.

Try also with the protein displayed as spacefill.  
Note the deep clefts in the myosin head.

With the protein displayed as cartoon, select protein sheet and specify a different color.
How many strands are in the b-sheet that is adjacent to the nucleotide binding site? 

Compare the overall shape of the protein and the location of the nucleotide-binding domain to the conformation depicted above.
Question: Can you duplicate the view above by simply rotating the protein?

To view the P-loop that makes contact with the nucleotide phosphates, select 176-182 and display sticks or ball & stick with color CPK.
Confirm the P-loop sequence of Gly-Glu-Ser-Gly-Ala-Gly-Lys (GESGAGK). 

The switch I segment at residues 237-244 (sequence NNNSSRFG) is one of two major switch regions that changes position as occupancy of the nucleotide binding site changes.
Select these residues, display as ball & stick and color CPK.
What is adjacent to the hydroxyls of the conserved serine residues in this sequence?

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