TAILIEUCHUNG - Báo cáo khoa học: NblA from Anabaena sp. PCC 7120 is a mostly a-helical protein undergoing reversible trimerization in solution

ThenblAfamily of genes encodes for small proteins neces-sary for the ordered degradation of phycobilisomes under certain stress conditions, a process known as chlorosis. Genes homologous tonblAseem to occur in all , todate, nomolecular mechanism is known for the action of NblA, nor have the gene products been characterized to understand the physical properties of the molecule and thus help elucidate the mechanism on a structural basis. | Eur. J. Biochem. 269 4617-4624 2002 FEBS 2002 doi NblA from Anabaena sp. PCC 7120 is a mostly a-helical protein undergoing reversible trimerization in solution Holaer Strauss1 Rolf Misselwitz2 Dirk Labudde1 Sabine Nicklisch3 and Kerstin Baier3 1Forschungsinstitut fur Molekulare Pharmakologie FMP Berlin Germany 2Max-DelbrUck-Centre fur Molekulare Medizin MDC Berlin Germany 3Humboldt Universitat zu Berlin Institut fur Biologie Biochemie der Pflanzen Germany The nblA family of genes encodes for small proteins necessary for the ordered degradation of phycobilisomes under certain stress conditions a process known as chlorosis. Genes homologous to nblA seem to occur in all phycobili-some-containing organisms. However to date no molecular mechanism is known for the action of NblA nor have the gene products been characterized to understand the physical properties of the molecule and thus help elucidate the mechanism on a structural basis. In this study we report on the first characterization of an NblA-homologous gene product. The chromosomal gene from the cyanobacterium Anabaena sp. PCC 7120 was cloned heterologously expressed in Escherichia coli and purified to apparent homogeneity. This allowed the protein to be characterized by analytical ultracentrifugation and CD spectroscopy. These experiments show that the NblA protein has a mostly a-helical structure undergoing an association reaction of folded monomers to form trimers in solution. No dimers are detectable. Keywords phycobilisome chlorosis NblA cyanobacteria analytical ultracentrifugation. Cyanobacteria are a widespread group of photosynthetic prokaryotes performing a plant-type oxygenic photosynthesis. They are very adaptable organisms that can survive in a wide variety of environmental conditions 1 2 . One limiting factor for growth is the nitrogen supply and cyanobacteria have developed various mechanisms to cope with this nutrient stress. One of the first responses exhibited by

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