tailieunhanh - Báo cáo khoa học: BchJ and BchM interact in a 1 : 1 ratio with the magnesium chelatase BchH subunit of Rhodobacter capsulatus

Substrate channeling between the enzymatic steps in the (bacterio)chloro-phyll biosynthetic pathway catalyzed by magnesium chelatase (BchI⁄ChlI, BchD⁄ChlD and BchH⁄ChlH subunits) andS-adenosyl-l-methionine:mag-nesium-protoporphyrin IX O-methyltransferase (BchM⁄ChlM) has been suggested. This involves delivery of magnesium-protoporphyrin IX from the BchH⁄ChlH subunit of magnesium chelatase to BchM⁄ChlM. | ỊFEBS Journal BchJ and BchM interact in a 1 1 ratio with the magnesium chelatase BchH subunit of Rhodobacter capsulatus Artur Sawicki and Robert D. Willows Department of Chemistry and Biomolecular Sciences Macquarie University Sydney NSW Australia Keywords bacteriochlorophyll biosynthesis BchJ BchM magnesium chelatase O-methyltransferase Correspondence R. D. Willows Department of Chemistry and Biomolecular Sciences Macquarie University NSW 2109 Australia Fax 6 298508245 Tel 6 298508146 E-mail Website http Received 23 December 2009 revised 11 August 2010 accepted 9 September 2010 doi Substrate channeling between the enzymatic steps in the bacteriochlorophyll biosynthetic pathway catalyzed by magnesium chelatase BchI ChlI BchD ChlD and BchH ChlH subunits and S-adenosyl-L-methionine mag-nesium-protoporphyrin IX O-methyltransferase BchM ChlM has been suggested. This involves delivery of magnesium-protoporphyrin IX from the BchH ChlH subunit of magnesium chelatase to BchM ChlM. Stimulation of BchM ChlM activity by BchH ChlH has previously been shown and physical interaction of the two proteins has been demonstrated. In plants and cyanobacteria there is an added layer of complexity as Gun4 serves as a porphyrin protoporphyrin IX and magnesium-protoporphy-rin IX carrier but this protein does not exist in anoxygenic photosynthetic bacteria. BchJ may play a similar role to Gun4 in Rhodobacter as it has no currently assigned function in the established pathway. Purified recombinant Rhodobacter capsulatus BchJ and BchM were found to cause a shift in the equilibrium amount of Mg-protoporphyrin IX formed in a magnesium chelatase assay. Analysis of this shift revealed that it was always in a 1 1 ratio with either of these proteins and the BchH subunit of the magnesium chelatase. The establishment of the new equilibrium was faster with BchM than with BchJ in a coupled magnesium chelatase assay. BchJ .