Structure of the Light Chain Binding Region

Given the pivotal role of the RLC in smooth muscle myosin s function, several important structural features of the LC binding domain and its relationship to myosin s catalytic or motor domain will first be described. The myosin HC, after emerging from the motor domain, forms a long 8.5-nm a-helix that is stabi- 

Despite considerable structural information, the structure of the N-terminal residues of the RLC and the location of the phosphorylatable serine are not known. In the crystal structure of the skeletal muscle myosin head, electron density was not observed for the N terminus of the RLC, suggesting that this region is flexible (Rayment et al., 1993). Density for the N terminus of the scallop myosin RLC begins six residues beyond the serine homologous to Ser 19 in the smooth RLC (Xie et al., 1994). In addition, scallop RLC lacks the N-terminal extension before the serine that contains the basic residues necessary for myosin light chain kinase binding. 

How information is transmitted between the neck and the active site remains a key unanswered question. It is noteworthy that the C-terminal 20-kDa portion of the HC extends throughout the length of the myosin head. It starts at a surface loop that is believed 

Copyright ) 1996 by Academic Press, Inc. All rights of reproduction in any form reserved. 

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