Dictyostelium discoideum plasma membranes contain an actin-nucleating activity that requires ponticulin, an integral membrane glycoprotein
UMass Chan Affiliations
Department of Cell BiologyDocument Type
Journal ArticlePublication Date
1990-03-01Keywords
ActinsAnimals
Carrier Proteins
Cell Membrane
Dictyostelium
Electrophoresis, Polyacrylamide Gel
Fungal Proteins
Kinetics
Macromolecular Substances
Membrane Glycoproteins
Microfilament Proteins
Muscles
Protein Binding
Rabbits
Spectrometry, Fluorescence
Cell Biology
Life Sciences
Medicine and Health Sciences
Metadata
Show full item recordAbstract
In previous equilibrium binding studies, Dictyostelium discoideum plasma membranes have been shown to bind actin and to recruit actin into filaments at the membrane surface. However, little is known about the kinetic pathway(s) through which actin assembles at these, or other, membranes. We have used actin fluorescently labeled with N-(1-pyrenyl)iodoacetamide to examine the kinetics of actin assembly in the presence of D. discoideum plasma membranes. We find that these membranes increase the rate of actin polymerization. The rate of membrane-mediated actin polymerization is linearly dependent on membrane protein concentrations up to 20 micrograms/ml. Nucleation (the association of activated actin monomers into oligomers) appears to be the primary step of polymerization that is accelerated. A sole effect on the initial salt-induced actin conformational change (activation) is ruled out because membranes accelerate the polymerization of pre-activated actin as well as actin activated in the presence of membranes. Elongation of preexisting filaments also is not the major step of polymerization facilitated by membranes since membranes stripped of all peripheral components, including actin, increase the rate of actin assembly to about the same extent as do membranes containing small amounts of endogenous actin. Acceleration of the nucleation step by membranes also is supported by an analysis of the dependence of polymerization lag time on actin concentration. The barbed ends of membrane-induced actin nuclei are not obstructed by the membranes because the barbed end blocking agent, cytochalasin D, reduces the rate of membrane-mediated actin nucleation. Similarly, the pointed ends of the nuclei are not blocked by membranes since the depolymerization rate of gelsolin-capped actin is unchanged in the presence of membranes. These results are consistent with previous observations of lateral interactions between membranes and actin filaments. These results also are consistent with two predictions from a model based on equilibrium binding studies; i.e., that plasma membranes should nucleate actin assembly and that membrane-bound actin nuclei should have both ends free (Schwartz, M. A., and E. J. Luna. 1988. J. Cell Biol. 107:201-209). Integral membrane proteins mediate the actin nucleation activity because activity is eliminated by heat denaturation, treatment with reducing agents, or proteolysis of membranes. Activity also is abolished by solubilization with octylglucoside but is reconstituted upon removal or dilution of the detergent. Ponticulin, the major actin-binding protein in plasma membranes, appears to be necessary for nucleation activity since activity is not reconstituted from detergent extracts depleted of ponticulin.Source
J Cell Biol. 1990 Mar;110(3):681-92. Link to article on publisher's website
DOI
10.1083/jcb.110.3.681Permanent Link to this Item
http://hdl.handle.net/20.500.14038/50752PubMed ID
2307703Related Resources
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Publisher PDF posted as allowed by the publisher's terms of use policy at: http://www.rupress.org/terms. After the Initial Publication Period, RUP will grant to the public the non-exclusive right to copy, distribute, or display the Article under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode, or updates thereof.Distribution License
http://creativecommons.org/licenses/by-nc-sa/4.0/ae974a485f413a2113503eed53cd6c53
10.1083/jcb.110.3.681
Scopus Count
Except where otherwise noted, this item's license is described as Publisher PDF posted as allowed by the publisher's terms of use policy at: http://www.rupress.org/terms. After the Initial Publication Period, RUP will grant to the public the non-exclusive right to copy, distribute, or display the Article under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 International license, as described at https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode, or updates thereof.