Journal Article

Plant Villin, Lily P-135-ABP, Possesses G-Actin Binding Activity and Accelerates the Polymerization and Depolymerization of Actin in a Ca<sup>2+</sup>-Sensitive Manner

Etsuo Yokota, Motoki Tominaga, Issei Mabuchi, Yasunori Tsuji, Christopher J. Staiger, Kazuhiro Oiwa and Teruo Shimmen

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 10, pages 1690-1703
Published in print October 2005 | ISSN: 0032-0781
Published online October 2005 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pci185
Plant Villin, Lily P-135-ABP, Possesses G-Actin Binding Activity and Accelerates the Polymerization and Depolymerization of Actin in a Ca2+-Sensitive Manner

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From germinating pollen of lily, two types of villins, P-115-ABP and P-135-ABP, have been identified biochemically. Ca2+-CaM-dependent actin-filament binding and bundling activities have been demonstrated for both villins previously. Here, we examined the effects of lily villins on the polymerization and depolymerization of actin. P-115-ABP and P-135-ABP present in a crude protein extract prepared from germinating pollen bound to a DNase I affinity column in a Ca2+-dependent manner. Purified P-135-ABP reduced the lag period that precedes actin filament polymerization from monomers in the presence of either Ca2+ or Ca2+-CaM. These results indicated that P-135-ABP can form a complex with G-actin in the presence of Ca2+ and this complex acts as a nucleus for polymerization of actin filaments. However, the nucleation activity of P-135-ABP is probably not relevant in vivo because the assembly of G-actin saturated with profilin, a situation that mimics conditions found in pollen, was not accelerated in the presence of P-135-ABP. P-135-ABP also enhanced the depolymerization of actin filaments during dilution-mediated disassembly. Growth from filament barbed ends in the presence of Ca2+-CaM was also prevented, consistent with filament capping activity. These results suggested that lily villin is involved not only in the arrangement of actin filaments into bundles in the basal and shank region of the pollen tube, but also in regulating and modulating actin dynamics through its capping and depolymerization (or fragmentation) activities in the apical region of the pollen tube, where there is a relatively high concentration of Ca2+.

Keywords: Actin; Calcium ion; Calmodulin; Lily pollen; Villin; CaM, calmodulin; P-115-ABP, plant 115-kDa actin bundling protein; P-135-ABP, plant 135-kDa actin bundling protein

Journal Article.  11627 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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