Structural studies on phycocyanins from three cyanobacterial spp. and xylanase from an alkalophilic bacillus sp.

Abstract

This thesis describes the research on C-phycocyanins (C-PC) from three cyanobacteria and an alkaline thermoactive xylanase (ATBXYL-C) from a Bacillus species. The first chapter involves a general introduction to the proteins under study, based on extensive review of available reports, publications and communications. The second chapter incorporates all the materials and methods employed in the course of the work. Next two chapters (3 & 4) record the results of various experiments on cyanobaterial phycocyanins, their analysis and comparison to existing knowledge. Similarly, last two chapters (5 & 6) involve documentation of results and relevant discussion about the xylanase. The major light-harvesting capacity of prokaryotic cyanobacteria and eukaryotic red algae is associated with large antennae complexes called phycobilisomes located on the surface of the photosynthetic thylakoid membranes. The phycobilisomes are composed of rods and a core, consisting of various phycobiliproteins and linker polypeptides. The phycobiliproteins are divided into three major classes: phycoerythrins, phycocyanins and allophycocyanins. The rods in phycobilisome normally have phycocyanin and the core has allophycocyanins. C-phycocyanins are composed of and subunits exhibiting high mutual affinity to form () monomers, which in turn aggregate into ()3 trimers and ()6 hexamers. Phycocyanins not only absorb light energy but also transfer the absorbed energy from phycoerythrins to allophycocyanins in the core and finally to the photosynthetic reaction center. In this thesis, we report the purification, crystallization and crystal structure analysis of C-PCs from the Indian cyanobacteria Phormidium and Lyngbya spp. Of marine habitat and Spirulina sp. of freshwater habitat. The crystal structure analysis of C-PCs has thrown light upon how the organization of C-PC units as seen in crystals helps in energy transfer. Xylanases produced by extremophiles are important due to their biotechnological applications and as model systems in structure-function studies. The paper and pulp industries use xylan-degrading enzymes for the pretreatment of paper pulp to enhance the bleaching effects. By using xylanases the quantity of bleaching chemicals can be reduced, thereby reducing the amount of toxic by-products and results in cost benefits also. Many studies on xylanases belonging to family G/11 have been reported.