• Asia/Kolkata
  • English
  • Login
iCal export
Chemical Sciences Seminars

Cyanobacterial Phycobiliproteins: A Comprehensive Study on Purification and Characterization

by Ms. Asha Parmar (Sardar Patel University, Gujarat)

Monday, August 8, 2011 from to (Asia/Kolkata)
at Colaba Campus ( AG-69 )
Description Cyanobacteria harvest light energy with macromolecular antennae complexes, termed phycobilisomes (PBS), consisting of two types of proteins: the phycobiliproteins (PBP) and the linker polypeptides. Phycobiliproteins are assembled from chromophore-appended dissimilar polypeptide chains belonging to two families (αand β) probably originating from a common ancestor but apparently diverged in evolution. The major phycobiliproteins, based on their spectral properties are, phycoerythrin (PE, λmax – 540-570 nm), phycocyanin (PC, λmax – 610-620 nm) and allophycocyanin (APC, λmax – 650-655 nm).
 
Phycoerythrin was successfully purified and characterized from Phormidium sp. A27DM and it was observed that the culture produced intact PE (with both αand ß-subunit) when they were young and produced truncated PE (14 kDa), after prolonged growth, which was also functional and continued to absorb light energy. This led to interesting questions such as that if truncated PE is functional than why at all the culture produces intact PE initially and what triggers formation of truncated protein. Thus various experiments like effect ofgrowth conditions, pH, absence of nitrogen source, proteases, acidic conditions on the subunit content of PE were studied to get the insights into the cleavage of an intact protein to its truncated form.The possible reasons can be proteases or self splicing mechanism or some other unknown mechanism. To check whether this phenomenon is universal or not, studies were done with different cyanobacterial cultures. Phormidium sp. A27DM and Halcomicronema sp. A32DM produced truncated 14 kDa fragment howeverLyngbya sp. A09DM never produced the same which concluded that this was not an universal phenomenon. The same three cultures were then studied to check the influence of light on their phycobiliprotein production. Lyngbya sp. A09DM was the best chromatically adapting culture which adapted well in all lights followed by Halomicronema sp. A32DM which adapted well in all lights except green light. Phormidium sp. A27DM was found to be the least chromatically adapting culture. The study signifies that light along with the nutrient availability plays a phenomenal role in adapting cyanobacteria to stress conditions. To get the complete insights into the functional aspects, structural analyses of phycoerythrins from Phormidium sp. A27DM and Lyngbya sp. A09DM were done. The toxicity studies were carried to prove the prospects of phycoerythrin for biotechnological applications.