OLIGOMERIZATION STATE OF RUBISCO ACTIVASE REVEALED BY DYNAMIC LIGHT SCATTERING

Authors: KIM, KANGMIN; PORTIS JR, ARCHIE

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/8/2002
Publication Date: 8/8/2002
Citation: Plant Biology 2002 Program: American SOciety of Plant Biologists Annual Meeting Abstract. 2002.

Interpretive Summary:

Technical Abstract: The self-association of Rubisco activase has been suggested to be required for Rubisco activation via ATP hydrolysis. To study the oligmerization patterns in detail, we initially measured the size of each isoform (42 KDa and 45 KDa) of recombinant spinach activase using dynamic light scattering spectroscopy. The particle size distribution of each isoform is polydisperse but shows a definite bimodal pattern. The average diameters of the two dominant populations are 17nm/111nm (42KDa) and 35 nm/168nm (45 KDa) and constant from 0.2 mg/ml to 10 mg/ml. The addition of MG++ with either ATP or ATP-y-S caused no change in the bimodal pattern but increased the proportion of the large-sized population. Conversely, addition of CHAPS (zwitterionic detergent) decreased the proportion of the large-sized population and reduced the ATPase activity of the 42 Kda isoform. This is consistent with previous evidence that oligomerization of activase increases its ATPase activity. To study the interaction between Rubisco and activase, we examined mixtures of the proteins. Spinach Rubsico alone exhibited a monodisperse size distribution (15 nm). The initial size estimation over short time period (2 min) for a mixture of Rubisco (inactive state) and the small activase isoform reflects their respective size distributions- 15 nm for Rubisco and 17 nm/111nm for activase. However, size measurements at extended times clearly showed formation of another larger-sized population of 341 nm, suggesting formation of a Rubisco-activase complex. Currently, we are performing SAXS (small angled X-ray scattering) studies, which will give more accurate information on particle size, shape and structures of Rubisco activase in the presence and absence of Rubisco in solution under various conditions.