CRYSTAL-STRUCTURE OF A VERTEBRATE SMOOTH-MUSCLE MYOSIN MOTOR DOMAIN AND ITS COMPLEX WITH THE ESSENTIAL LIGHT-CHAIN - VISUALIZATION OF THE PRE-POWER STROKE STATE

The crystal structures of an expressed vertebrate smooth muscle myosin motor domain (MD) and a motor domain-essential light chain (ELC) comp lex (MDE), both with a transition state analog (MgADP . AlF4-) in the active site, have been determined to 2.9 Angstrom and 3.5 Angstrom res olution, respectively. The MDE structure with an ATP analog (MgADP . B eFx) was also determined to 3.6 Angstrom resolution. In all three stru ctures, a domain of the C-terminal region, the ''converter,'' is rotat ed similar to 70 degrees from that in nucleotide-free skeletal subfrag ment 1 (S1). We have found that the MDE-BeFx and MDE-AlFx structures a re almost identical, consistent with the fact that they both bind weak ly to actin. A comparison of the lever arm positions in MDE-AlF4- and in nucleotide-free skeletal S1 shows that a potential displacement of similar to 10 nm can be achieved during the power stroke.