Sun, 20 Jul 2008 13:42:52 BST CiteULike: cactus Knight http://www.citeulike.org/user/cactus/author/Knight CiteULike.org en-gb Copyright © 2004-2008 citeulike.org http://www.citeulike.org/user/cactus/article/2763966 <i>Proceedings of the National Academy of Sciences, Vol. 105, No. 16. (22 April 2008), pp. 6022-6026.</i><br /><br />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. 10.1073/pnas.0707846105 Conservation of the regulated structure of folded myosin 2 in species separated by at least 600 million years of independent evolution Hyun Jung Stan Burgess Neil Billington Melanie Colegrave Hitesh Patel Joseph Chalovich Peter Chantler Peter Knight doi:10.1073/pnas.0707846105 Proceedings of the National Academy of Sciences, Vol. 105, No. 16. (22 April 2008), pp. 6022-6026. 2008-05-07T06:28:28-00:00 2008 Proceedings of the National Academy of Sciences 105 16 6022 6026 clip em myosin structure http://www.citeulike.org/user/cactus/article/1375303 <i>Proc Natl Acad Sci U S A (4 June 2007)</i><br /><br />Loads on molecular motors regulate and coordinate their function. In a study that directly measures properties of internally strained myosin 2 heads bound to actin, we find that human nonmuscle myosins 2A and 2B show marked load-dependent changes in kinetics of ADP release but not in nucleotide binding. We show that the ADP release rate constant is increased 4-fold by the assisting load on one head and decreased 5-fold (for 2A) or 12-fold (for 2B) by the resisting load on the other. Thus these myosins, especially 2B, have marked mechanosensitivity of product release. By regulating the actin attachment of myosin heads, this provides a basis for energy-efficient tension maintenance without obstructing cellular contractility driven by other motors such as smooth muscle myosin. Whereas forward load accelerates the cycle of interaction with actin, resistive load increases duty ratio to favor tension maintenance by two-headed attachment. Load-dependent mechanism of nonmuscle myosin 2. Mihály Kovács Kavitha Thirumurugan Peter J Knight James R Sellers doi:10.1073/pnas.0701181104 Proc Natl Acad Sci U S A (4 June 2007) 2007-06-10T03:12:44-00:00 2007 Proc Natl Acad Sci U S A 0027-8424 adp experiment motor myosin strain