Essential and Regulatory Myosin Light Chains (ELC, RLC)

displayed: ELC N-terminal domain in light grey, C-terminal domain in light pink; RLC N-terminal domain in dark grey, C-terminal domain in dark pink (1WDC).
The regulatory domain of myosin consists of a heavy-chain fragment (HC), the ELC and the RLC.  The ELC wraps around the N-terminal end of the HC, while the RLC binds to the C-terminal end.  The N-terminal domain EF-hands (EF1, EF2) of ELC are in the closed conformation (like Ca2+-free CaM and TnC); it is interesting to note that only ELC EF1 binds Ca2+, yet it still forms a closed conformation.  ELC EF2 is rather unusual in its position, and is the only EF-hand of the light chains not making contact with the HC.  The N-terminal domain EF-hands of RLC are in the open conformation (Ca2+-CaM, Ca2+-TnC), and RLC EF1 binds a Mg2+ ion.  The C-terminal domain EF-hands (EF3, EF4) of both light chains - none of which bind metal ions - assume a semi-open conformation in which the helices are not as far apart as in the open conformation, not as close together as in the closed conformation.  However, this conformation is not characterised by uniform values of phi, theta and omega as in the open and closed conformations, nor do the values indicate that the semi-open conformation is an intermediate between the two.

EF-hand (helix residues) N-terminal coordinate
of second helix
theta phi omega
ELC EF1 (11-18, 30-40) (11.192, -0.587, -2.606) 42.224 118.519 112
ELC EF2 (46-53, 65-75) (2.353, 11.068, -7.121) 43.166 -160.151 23
ELC EF3 (86-93, 103-113) (10.557, -3.027, -4.187) 62.039 75.110 167
ELC EF4 (122-129, 141-151) (12.036, -0.420, -2.217) 90.230 123.055 144
RLC EF1 (20-27, 37-47) (6.755, -0.829, -8.174) 85.201 106.902 81
RLC EF2 (56-63, 69-79) (9.145, 2.622, -6.354) 84.804 127.200 80
RLC EF3 (89-96, 106-116) (10.015, -5.325, -4.848) 73.995 62.202 196
RLC EF4 (125-132, 141-151) (7.449, 6.707, -5.399) 83.304 135.244 158


NB: values obtained using apo-CaM EF1 (as in refcam.pdb) as the reference EF-hand.

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