Chae, Keun , Zhang, Kangling , Zhang, Li , Morikis, Dimitrios , Kim, Suntae , Mollet, Jean-Claude , Lord, Elizabeth .
A relationship between structural features and lily pollen tube adhesion activity of SCA (Stigma/style Cysteine-rich Adhesin) isoforms.
Lily pollen tubes grow adhering to an extracellular matrix produced by the transmitting tract epidermis in a hollow style. SCA, a small (~ 9.4 kDa) and basic protein, and low-esterified pectin were previously identified to be involved in the pollen tube adhesion event. However, its mode of action is unknown. We purified three SCA isoforms with a partial separation, from the lily stigma in serial size-exclusion column fractions (SCA1: 9370 Da, SCA2: 9384 Da, SCA3: 9484 Da). Peptide sequencing analysis allowed us to determine two amino acid variations in SCA3, compared to SCA1: Arg26 and Ala71. For SCA2, however, there are more sequence variations yet to be identified. Our structural homology and molecular dynamics (MD) modeling results show that SCA isoforms have the typical structure of the plant non-specific lipid transfer protein (nsLTP) family: a globular shape of the orthogonal 4-helix bundle architecture, four disulfide bonds, a hydrophobic core, an internal hydrophobic and solvent inaccessible cavity, and a long C-terminal tail in random coil conformations. Arg26 in SCA3, replacing Gly26 in SCA1, is predicted to cause structural changes that result in a significantly reduced volume for the internal hydrophobic cavity in SCA3. The volume of the internal cavity fluctuates slightly during the MD simulation, but overall, SCA1 displays a larger cavity than SCA3. SCA1 displays the highest activity in the in vitro pollen tube adhesion assay amongst the SCA isoforms. No differences were found amongst SCAs in a binding assay with pectin. The correlation between the larger size of the hydrophobic cavity in SCA1 and its higher adhesion activity suggests that the structure of this isoform, which is the most abundant in the pistil, has a relation to its function in enhancing pollen tube adhesion activity.
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1 - University of California Riverside, 4477 Picacho Dr, Riverside, California, 92507, USA
2 - University of Californai, Riverside, Chemistry
3 - University of California, Riverside, Chemistry
4 - University of California, Riverside, Bioengineering
5 - Kyungsang University, Korea, Environmental Biotechnology Research Center
6 - Université d’Artois, France, Laboratoire de Glycobiologie et Physiologie Végétale
7 - University of California, Riverside, Botany and Plant Science
pollen tube adhesion
SCA (Stigma/style Cysteine-rich Adhesin).
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM