A novel protein accumulated during maturation of the pods of the plantImpatiens balsamina

Pal, Manisha; Biswas, Sumit

doi:10.1007/bf01457392

Cited by 7 publications

(2 citation statements)

References 48 publications

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“…Other than a 75-kDa glycoprotein purified from Impatiens fruit pods (57), there is no prior evidence for capping protein activity in plants. This unidentified protein is an apparent homotetramer that inhibits actin polymerization in seeded elongation reactions.…”

Section: Discussionmentioning

confidence: 99%

Arabidopsis Capping Protein (AtCP) Is a Heterodimer That Regulates Assembly at the Barbed Ends of Actin Filaments

Huang

Blanchoin

Kovar

et al. 2003

Journal of Biological Chemistry

137

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The precise regulation of actin filament polymerization and depolymerization is essential for many cellular processes and is choreographed by a multitude of actinbinding proteins (ABPs). In higher plants the number of well characterized ABPs is quite limited, and some evidence points to significant differences in the biochemical properties of apparently conserved proteins. Here we provide the first evidence for the existence and biochemical properties of a heterodimeric capping protein from Arabidopsis thaliana (AtCP). The purified recombinant protein binds to actin filament barbed ends with K d values of 12-24 nM, as assayed both kinetically and at steady state. AtCP prevents the addition of profilin actin to barbed ends during a seeded elongation reaction and suppresses dilution-mediated depolymerization. It does not, however, sever actin filaments and does not have a preference for the source of actin. During assembly from Mg-ATP-actin monomers, AtCP eliminates the initial lag period for actin polymerization and increases the maximum rate of polymerization. Indeed, the efficiency of actin nucleation of 0.042 pointed ends created per AtCP polypeptide compares favorably with mouse CapZ, which has a maximal nucleation of 0.17 pointed ends per CapZ polypeptide. AtCP activity is not affected by calcium but is sensitive to phosphatidylinositol 4,5-bisphosphate. We propose that AtCP is a major regulator of actin dynamics in plant cells that, together with abundant profilin, is responsible for maintaining a large pool of actin subunits and a surprisingly small population of F-actin.The cytoskeleton in plant cells comprises a dynamic network of actin filaments, microtubules, and accessory proteins that powers cytoplasmic streaming, responds rapidly to prevent fungal attack, patterns the deposition of cellulosic wall polymers, and shapes cellular morphogenesis by choreographing exo-and endocytotic vesicle traffic. Understanding how the cytoskeleton is organized, how it responds to extrinsic and intrinsic cues, and how dynamics are regulated are central questions in plant biology (1). To date less than a dozen of the more than 70 classes of actin-binding proteins (ABPs) 1 found in eukaryotic cells (2, 3) have been isolated and characterized from plants. Particularly well studied are members of the profilin, ADF/cofilin, fimbrin, villin, EF-1␣, and myosin families (4, 5). Although the general properties of ABPs are often conserved across kingdoms, important differences highlight the need to examine in detail the functional properties of proteins from divergent organisms. For example, Chlamydomonas profilin binds extremely poorly to one of the major known ligands (poly-L-proline) and inhibits nucleotide exchange on actin (6), and phylogenetically unique classes of plant myosins are the fastest molecular motors on the planet (7). Based on genome sequencing, many classes of ABP are missing from higher plants, including ␣-actinin, spectrin, tropomyosin, WASp, and coronin (4,8). One intriguing possibility is that multiple iso...

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Section: Discussionmentioning

confidence: 99%

Arabidopsis Capping Protein (AtCP) Is a Heterodimer That Regulates Assembly at the Barbed Ends of Actin Filaments

Huang

Blanchoin

Kovar

et al. 2003

Journal of Biological Chemistry

137

View full text Add to dashboard Cite

show abstract

“…A high molecular weight protein has been isolated as a major polypeptide comprising 85 % of the total extractable proteins in balsam fruit pericarp (Pal and Biswas 1994 ). This protein appeared to be a homo-tetramer consisting of subunits, Mr 75 K. Four closely related highly basic, antimicrobial peptides of 20 amino acids long, containing four cysteine residues forming two intramolecular disulfi de bonds, designated Ib-AMP1, Ib-AMP2, Ib-AMP3 and Ib-AMP4 (Tailor et al 1997 ) and Ib-AMP1 and Ib-AMP4 peptides, were isolated from the seeds (Thevissen eYIb-AMP1, a highly basic, 20-residue peptide was found to have fi ve arginine residues and to contain four cysteines forming two intramolecular disulfi de bonds (Patel et al 1998 ).…”

Section: Fruit/seed Phytochemicalsmentioning

confidence: 99%