Abstract
The Arp2/3 complex creates filament branches leading to an enhancement in the rate of actin polymerization. Work with Arp complexes from different sources indicated that it was inactive by itself, required an activating factor such as the Wiskott-Aldrich syndrome protein (WASP), and might exhibit a preference for ATP or ADP-P(i) actin. However, with yeast actin, P(i) release is almost concurrent with polymerization, eliminating the presence of an ADP-P(i) cap. We thus investigated the ability of the yeast Arp2/3 complex (yArp2/3) to facilitate yeast actin polymerization in the presence and absence of the Arp2/3-activating factor Las17p WA. yArp2/3 significantly accelerates yeast actin but not muscle actin polymerization in the absence of Las17p WA. The addition of Las17p WA further enhances yeast actin polymerization by yArp2/3 and allows the complex to now assist muscle actin polymerization. This actin isoform difference is not observed with bovine Arp2/3 complex, because the neural WASP VCA fragment is required for polymerization of both actins. Observation of individual branching filaments showed that Las17p WA increased the persistence of filament branches. Compared with wild type actin, the V159N mutant actin, proposed to be more ATP-like in behavior, exhibited an enhanced rate of polymerization in the presence of the yArp2/3 complex. yArp2/3 caused a significant rate of P(i) release prior to observation of an increase in filament mass but while branched structures were present. Thus, yeast F-actin can serve as a primary yArp2/3-activating factor, indicating that a newly formed yeast actin filament has a topology, unlike that of muscle actin, that is recognized specifically by yArp2/3.
Highlights
The proper functioning of the actin cytoskeleton in processes such as cytokinesis [1], cell motility [2, 3], endocytosis and exocytosis [4, 5], and lamellipodial extension [6, 7] requires that the system be dynamic both temporally and spatially
Yeast Actin Polymerization in the Presence of yArp2/3 and Las17p WA—To begin to characterize the biochemical behavior of the yeast actin/yeast Arp2/3 complex system, we assessed the relative ability of yArp2/3 alone to promote the polymerization of yeast versus muscle actin
A similar observation was recently published in a paper dealing with the effect of Pan1p on Arp2/3 function, no comment was made on the differential effect of the muscle and yeast actins on yArp2/3 activity [19]
Summary
The proper functioning of the actin cytoskeleton in processes such as cytokinesis [1], cell motility [2, 3], endocytosis and exocytosis [4, 5], and lamellipodial extension [6, 7] requires that the system be dynamic both temporally and spatially. We investigated the ability of the yeast Arp2/3 complex (yArp2/3) to facilitate yeast actin polymerization in the presence and absence of the Arp2/3-activating factor Las17p WA.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
