TY - JOUR
T1 - Structure of the Cyanobacterial Magnesium Chelatase H Subunit Determined by Single Particle Reconstruction and Small-angle X-ray Scattering
AU - Qian, Pu
AU - Marklew, Christopher J.
AU - Viney, Joanne
AU - Davison, Paul A.
AU - Brindley, Amanda A.
AU - Söderberg, Christopher
AU - Al-Karadaghi, Salam
AU - Bullough, Per A.
AU - Grossmann, J. Guenter
AU - Hunter, C. Neil
PY - 2012
Y1 - 2012
N2 - The biosynthesis of chlorophyll, an essential cofactor for photosynthesis, requires the ATP-dependent insertion of Mg2+ into protoporphyrin IX catalyzed by the multisubunit enzyme magnesium chelatase. This enzyme complex consists of the I subunit, an ATPase that forms a complex with the D subunit, and an H subunit that binds both the protoporphyrin substrate and the magnesium protoporphyrin product. In this study we used electron microscopy and small-angle x-ray scattering to investigate the structure of the magnesium chelatase H subunit, ChlH, from the thermophilic cyanobacterium Thermosynechococcus elongatus. Single particle reconstruction of negatively stained apo-ChlH and Chl-porphyrin proteins was used to reconstitute three-dimensional structures to a resolution of similar to 30 angstrom. ChlH is a large, 148-kDa protein of 1326 residues, forming a cage-like assembly comprising the majority of the structure, attached to a globular N-terminal domain of similar to 16 kDa by a narrow linker region. This N-terminal domain is adjacent to a 5 nm-diameter opening in the structure that allows access to a cavity. Small-angle x-ray scattering analysis of ChlH, performed on soluble, catalytically active ChlH, verifies the presence of two domains and their relative sizes. Our results provide a basis for the multiple regulatory and catalytic functions of ChlH of oxygenic photosynthetic organisms and for a chaperoning function that sequesters the enzyme-bound magnesium protoporphyrin product prior to its delivery to the next enzyme in the chlorophyll biosynthetic pathway, magnesium protoporphyrin methyltransferase.
AB - The biosynthesis of chlorophyll, an essential cofactor for photosynthesis, requires the ATP-dependent insertion of Mg2+ into protoporphyrin IX catalyzed by the multisubunit enzyme magnesium chelatase. This enzyme complex consists of the I subunit, an ATPase that forms a complex with the D subunit, and an H subunit that binds both the protoporphyrin substrate and the magnesium protoporphyrin product. In this study we used electron microscopy and small-angle x-ray scattering to investigate the structure of the magnesium chelatase H subunit, ChlH, from the thermophilic cyanobacterium Thermosynechococcus elongatus. Single particle reconstruction of negatively stained apo-ChlH and Chl-porphyrin proteins was used to reconstitute three-dimensional structures to a resolution of similar to 30 angstrom. ChlH is a large, 148-kDa protein of 1326 residues, forming a cage-like assembly comprising the majority of the structure, attached to a globular N-terminal domain of similar to 16 kDa by a narrow linker region. This N-terminal domain is adjacent to a 5 nm-diameter opening in the structure that allows access to a cavity. Small-angle x-ray scattering analysis of ChlH, performed on soluble, catalytically active ChlH, verifies the presence of two domains and their relative sizes. Our results provide a basis for the multiple regulatory and catalytic functions of ChlH of oxygenic photosynthetic organisms and for a chaperoning function that sequesters the enzyme-bound magnesium protoporphyrin product prior to its delivery to the next enzyme in the chlorophyll biosynthetic pathway, magnesium protoporphyrin methyltransferase.
U2 - 10.1074/jbc.M111.308239
DO - 10.1074/jbc.M111.308239
M3 - Article
C2 - 22179610
SN - 1083-351X
VL - 287
SP - 4946
EP - 4956
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 7
ER -