Profilins are low-molecular-mass (12–15kDa) cytosolic proteins that are major regulators of actin assembly in all eukaryotic cells. In general, profilins from evolutionarily diverse organisms share the ability to bind to G-actin, poly-(l-proline) (PLP) and proline-rich proteins, and polyphosphoinositides. However, the functional importance of each of these interactions remains unclear and might differ between organisms. We investigated the importance of profilin's interaction with its various ligands in plant cells by characterizing four maize (Zea mays) profilin 5 (ZmPRO5) mutants that had single amino acid substitutions in the presumed sites of ligand interaction. Comparisons in vitro with wild-type ZmPRO5 showed that these mutations altered ligand association specifically. ZmPRO5-Y6F had a 3-fold increased affinity for PLP, ZmPRO5-Y6Q had a 5-fold decreased affinity for PLP, ZmPRO5-D8A had a 2-fold increased affinity for PtdIns(4,5)P2 and ZmPRO5-K86A had a 35-fold decreased affinity for G-actin. When the profilins were microinjected into Tradescantia stamen hair cells, ZmPRO5-Y6F increased the rate of nuclear displacement in stamen hairs, whereas ZmPRO5-K86A decreased the rate. Mutants with a decreased affinity for PLP (ZmPRO5-Y6Q) or an enhanced affinity for PtdIns(4,5)P2 (ZmPRO5-D8A) were not significantly different from wild-type ZmPRO5 in affecting nuclear position. These results indicate that plant profilin's association with G-actin is extremely important and further substantiate the simple model that profilin acts primarily as a G-actin-sequestering protein in plant cells. Furthermore, interaction with proline-rich binding partners might also contribute to regulating profilin's effect on actin assembly in plant cells.
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August 2001
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Research Article|
August 08 2001
The characterization of ligand-specific maize (Zea mays) profilin mutants
David R. KOVAR;
David R. KOVAR
∗Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, U.S.A.
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Bj⊘rn K. DRØBAK;
Bj⊘rn K. DRØBAK
†Cell Signalling Group, Department of Disease and Stress Biology, John Innes Centre, Norwich NR4 7UH, U.K.
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David A. COLLINGS;
David A. COLLINGS
1
∗Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, U.S.A.
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Christopher J. STAIGER
Christopher J. STAIGER
2
∗Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, U.S.A.
2To whom correspondence should be addressed (e-mail cstaiger@bilbo.bio.purdue.edu).
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Publisher: Portland Press Ltd
Received:
April 17 2001
Revision Received:
May 22 2001
Accepted:
June 15 2001
Online ISSN: 1470-8728
Print ISSN: 0264-6021
The Biochemical Society, London ©2001
2001
Biochem J (2001) 358 (1): 49–57.
Article history
Received:
April 17 2001
Revision Received:
May 22 2001
Accepted:
June 15 2001
Citation
David R. KOVAR, Bj⊘rn K. DRØBAK, David A. COLLINGS, Christopher J. STAIGER; The characterization of ligand-specific maize (Zea mays) profilin mutants. Biochem J 15 August 2001; 358 (1): 49–57. doi: https://doi.org/10.1042/bj3580049
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