Dicty News Electronic Edition Volume 24, number 13 May 20, 2005 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of Dicty-News, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. ============= Abstracts ============= The Diaphanous-related Formin dDia2 is Required for the Formation and Maintenance of Filopodia Antje Schirenbeck (1), Till Bretschneider (2), Rajesh Arasada (1), Michael Schleicher (1), and Jan Faix (1) 1) A. Butenandt-Institut / Zellbiologie, Ludwig-Maximilians-UniversitŠt, Schillerstr. 42, 80336 MŸnchen, Germany. 2) AG Zelldynamik, Max-Planck-Institut fŸr Biochemie, Am Klopferspitz 18a, 82152 Martinsried, Germany. Nature Cell Biology, in press Formins play important roles in the nucleation of actin and the formation of linear actin filaments, yet their role in filopodium formation has remained elusive. Dictyostelium Diaphanous-related formin dDia2 is enriched at the tips of filopodia and interacts with profilin II and Rac1. An FH1FH2 fragment of dDia2 nucleated actin polymerization and removed capping protein from capped filament ends. Genetic studies showed that dDia2 is important for cell migration as well as the formation, elongation and maintenance of filopodia. Here we provide evidence that dDia2 specifically controls filopodial dynamics by regulating actin turnover at the barbed ends of actin filaments. Submitted by: Jan Faix [faix@bpc.mh-hannover.de] ----------------------------------------------------------------------------- Biological, Biochemical and Kinetic Effects of Mutations of the Cardiomyopathy-loop of Dictyostelium Myosin II: Importance of Ala400 Xiong Liu*, Shi Shu*, Mih‡ly Kov‡cs , and Edward D. Korn Laboratory of Cell Biology, and  Laboratory of Molecular Physiology National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892 Running title: Dictyostelium myosin II CM-loop mutants Address correspondence to: Edward D. Korn, Laboratory of Cell Biology, NHLBI, NIH, Building 50, Room 2517-8017, Bethesda, MD 20892-8017, Tel. 301-496-1616; Fax. 301-402-1519; E-mail: edk@nih.gov *XL and SS contributed equally to this work. Journal of biological Chemistry, in press (available on-line May 16th) The cardiomyopathy (CM)-loop of the heavy chain of class-II myosins begins with a highly conserved Arg residue (whose mutation in human beta-cardiac myosin II results in familial hypertrophic cardiomyopathy). The CM-loop of Dictyostelium myosin II (R397-Q407) is essential for its biological functions and biochemical activities. We found that the CM-loop of smooth muscle myosin II substituted partially and the CM-loop of beta-cardiac myosin II much less well for growth, capping of surface receptors and development, and the actin-activated MgATPase and in vitro motility activities of purified myosins. There was little correlation between the biochemical and biological activities of the two chimeras and 19 point mutants but only the five mutants with kcat/Kactin values equivalent to wild-type myosin supported essentially full biological function. The three point mutations of R397 equivalent to those that result in hypertrophic cardiomyopathy in humans had minimal biological effects and different biochemical effects. The A400V mutation rendered full-length wild-type myosin almost completely inactive, both in vitro and in vivo, and the reverse V400A mutation in the cardiac CM-loop chimera restored almost full activity, even though the sequence still differed from wild-type in 7 of 11 positions. Transient kinetic studies of acto-subfragment-1 (S1) showed that the chimeras and the Ala/Val, Val/Ala mutations do not affect the equilibrium or the association and dissociation rate constants for either ATP or ADP binding to acto-S1 or the rate of ATP-induced dissociation of acto-S1. We conclude that the Ala/Val, Val/Ala mutations affect the release of Pi from acto-S1áADPáPi. In addition, Val at position 400 substantially reduces the affinity of actin for S1 in the absence of nucleotide. Submitted by: Korn, Edward [korned2@nhlbi.nih.gov] ============================================================================== [End Dicty News, volume 24, number 13]