Conservation of the regulated structure of folded myosin 2 in species separated by at least 600 million years of independent evolution - PubMed (original) (raw)

Comparative Study

. 2008 Apr 22;105(16):6022-6.

doi: 10.1073/pnas.0707846105. Epub 2008 Apr 14.

Affiliations

Comparative Study

Conservation of the regulated structure of folded myosin 2 in species separated by at least 600 million years of independent evolution

Hyun Suk Jung et al. Proc Natl Acad Sci U S A. 2008.

Abstract

The myosin 2 family of molecular motors includes isoforms regulated in different ways. Vertebrate smooth-muscle myosin is activated by phosphorylation of the regulatory light chain, whereas scallop striated adductor-muscle myosin is activated by direct calcium binding to its essential light chain. The paired heads of inhibited molecules from myosins regulated by phosphorylation have an asymmetric arrangement with motor-motor interactions. It was unknown whether such interactions were a common motif for inactivation used in other forms of myosin-linked regulation. Using electron microscopy and single-particle image processing, we show that indistinguishable structures are indeed found in myosins and heavy meromyosins isolated from scallop striated adductor muscle and turkey gizzard smooth muscle. The similarities extend beyond the shapes of the heads and interactions between them: In both myosins, the tail folds into three segments, apparently at identical sites; all three segments are in close association outside the head region; and two segments are associated in the same way with one head in the asymmetric arrangement. Thus, these organisms, which have different regulatory mechanisms and diverged from a common ancestor >600 Myr ago, have the same quaternary structure. Conservation across such a large evolutionary distance suggests that this conformation is of fundamental functional importance.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Compact conformation of ScHMM. Examples of averaged images showing compact ScHMM molecules in right (A) and left (C) views, obtained from 239 and 68 compact molecules, respectively, classified by using head region features. (B and D) Corresponding projection images of the atomic model of SmHMM (12) (1i84.pdb, as modified (13) and with the tail portion removed). Adjacent cartoons show the boundary of each head in the atomic model drawn as outlines with the blocked head shaded black and the free head in white. (E) Averaged images from classification of the proximal part of the ScHMM tail region; white arrow points to the emergence of the tail from the head region. (F) Ribbon representation of B; heavy chains blue, ELC orange, RLC green, free head depicted in paler colors; α-carbon of Ile-792 (the “pliant point”) in the blocked head heavy chain depicted as a sphere, colored red, and labeled; α-carbon of proline in heavy chain near the tip of each lever depicted as a red sphere. (G) Atomic model of two scallop myosin heads containing ADP and vanadate (1dfl.pdb), colored as in F; motor domains arranged by superposition on those of the SmHMM model (F). Note that the pliant point (Leu-778 in the scallop sequence) is unbroken α-helix, and the levers therefore diverge instead of converge. The free head shows a lesser effect of this difference in pliant-point structure, because the plane of bending is almost aligned with this direction of view. Images in A–D, 26.5 nm wide. (Scale bar in E: 20 nm.)

Fig. 2.

Fig. 2.

Structure of folded ScM. (A and B) Averaged images of the compact conformation of ScM showing right and left views, respectively. The arrow indicates the free-head motor domain and the arrowhead indicates the prominent spot beside the blocked-head lever domain. (C and D) Image subtractions to reveal the path of the folded tail in the head region in right and left views, respectively. Arrowheads in left and right panels indicate the second bend in the tail. (Left) ScM averages (averaged from 702 and 497 molecules, respectively). (Center) Coaligned compact ScHMM averages (averaged from 239 and 68 molecules, respectively). (Right) ScHMM average subtracted from ScM average. Class numbers and the number of images combined in each average in A and B are shown in the upper left and lower right of each panel, respectively. (Scale bar in A: 20 nm.)

Fig. 3.

Fig. 3.

Comparison of the compact conformations of ScM and SmM. (A and C) Averaged right-view images of ScHMM (A) and SmHMM (C) (183 images of each). (D and F) Averaged right-view images of ScM (D) and SmM (F) (491 images of each). (G and I) Averaged left-view images of ScM (G) and SmM (I) (303 images of each). (B) The right-view images of ScHMM and SmHMM were grouped together, aligned, and classified by using head-region features into eight classes. These are ranked in order of increasing proportion of SmHMM images. (E and H) Right- and left-view images of ScM and SmM treated similarly. Histogram in lower left of each image within the montages (B, E, and H) shows the number of SmHMM or SmM (left bar) and ScM or ScHMM (right bar) images ascribed to each class. Arbitrary class number and number of images contributing to each average are shown in the upper left and lower right corners of each image, respectively. The white arrow in H points to the separated region of the tail seen principally in SmM images. Images in A, C, D, F, G, and I are 31.8 nm wide; B, E, and H are 42.4 nm wide.

Fig. 4.

Fig. 4.

Folding and flexibility of the tail in regulated myosins. (A and C) Representative averaged images of ScM in right and left views, respectively. (B and D) Averaged images of SmM comparable with those seen in A and B. (Scale bar in A: 20 nm.) See also

Movies S1

–

S4

.

References

    1. Craig R, Padrón R. In: Myology. Engel AG, Franzini-Armstrong C, editors. Vol 1. New York: McGraw-Hill; 2004. pp. 129–166.
    1. Robinson DN, Spudich JA. Mechanics and regulation of cytokinesis. Curr Opin Cell Biol. 2004;16:182–188. - PMC - PubMed
    1. Chantler PD, Wylie SR. Elucidation of the separate roles of myosins IIA and IIB during neurite outgrowth, adhesion and retraction. IEE Proc Nanobiotechnol. 2003;150:111–125. - PubMed
    1. Sellers JR. Myosins. Oxford: Oxford Univ Press; 1999.
    1. Houdusse A, Cohen C. Structure of the regulatory domain of scallop myosin at 2 Å resolution: Implications for regulation. Structure (London) 1996;4:21–32. - PubMed

Publication types

MeSH terms

Substances

LinkOut - more resources