ISSN:
1615-6102
Keywords:
Actin
;
Actin-binding protein
;
Cytoskeleton
;
Immunogold
;
Pollen tube
;
Rapid-freeze fixation
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary Actin microfilaments, which are essential for cell growth and cytoplasmic streaming in pollen tubes, are closely dependent on actin-binding proteins for their organization and regulation. We have purified the plant 135 kDa actin-bundling protein (P-135-ABP) fromLilium longiflorum pollen and determined that its amino acid composition is highly similar to members of the villin-gelsolin family of proteins. We used antibodies against P-135-ABP to probe an expression cDNA library ofL. longiflorum pollen and isolated a full-length clone (ABP135) that corresponds to a 106 kDa polypeptide. The deduced amino acid sequence ofABP135 shows homology with members of the villin-gelsolin family of proteins and contains the characteristic six repeats of this family, as well as an extended carboxy-terminal domain that includes the villin headpiece preceded by a highly variable region. Using two-dimensional polyacrylamide gel electrophoresis we detected at least 5 isoforms of P-135-ABP, with isoelectric points (pI) ranging between 5.6 to 5.9. The most abundant P-135-ABP isoform has a pI of 5.8, closely approximating the pI predicted from the deducedABP135 amino acid sequence. These data, together with the partial amino acid sequence from a proteolytic peptide of the protein, indicate that P-135-ABP is a plant villin. Immuno-detection of Lilium villin in rapidly frozen pollen tubes localized it to actin bundles. Lilium villin is also ubiquitously expressed in all tissues tested. Since villins, like gelsolins, are also Ca2+-dependent severing, capping, and nucleating proteins, Lilium villin may participate in F-actin fragmentation and nucleation in the apex of the pollen tube where there is steep Ca2+ gradient.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01453456
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