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Preliminary structural studies of ribulose-1,5-bisphosphate carboxylase/oxygenase from Rhodospirillum rubrum.

1984; Elsevier BV; Volume: 259; Issue: 18 Linguagem: Inglês

10.1016/s0021-9258(18)90904-x

1083-351X

Cheryl A. Janson, Ward W. Smith, David Eisenberg, F.C. Hartman,

Photosynthetic Processes and Mechanisms

Ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39)from Rhodospirillum rubrum has been crystallized in a form that is suitable for structural studies by x-ray diffraction.The asymmetric unit of the crystal contains one dimeric enzyme molecule of molecular mass 101,000 Da.The enzyme was activated prior to crystallization and is presumed to be in the C02-activated state in the crystal.The method of hydrophobicity correlation has been used to compare the amino acid sequence of this molecule (466 residues) to that of the large subunit of a higher plant ribulose-1,5-bisphosphate carboxylase/ oxygenase (477 residues in Nicotiana tabacum).The pattern of residue hydrophobicities is similar along the two polypeptides.This suggests that the three-dimensional folding of the large polypeptide chains may be similar in plant and bacterial enzymes.If this is so, knowing the structure of either the plant or bacterial ribulose-1,5-bisphosphate carboxylasefoxygenase should aid in learning the structure of the other.Ribulose-1,5-bisphosphate carboxylase/oxygenase catalyzes the initial step of the Calvin reductive pentose phosphate cycle, and is the most abundant protein on earth (1; see Ref. 2 for a review).The enzyme also catalyzes the first metabolic step in the competing pathway of photorespiration.Hence, understanding and perhaps modifying its structure may improve crop yields.The enzyme is found both in higher plants and in a variety of photosynthetic microorganisms.The ribulose-1,5-bisphosphate carboxylase/oxygenase from the purple non-sulfur bacterium Rhodospirillum rubrum has been studied extensively (3-8) and its amino acid sequence is known (9-11).The enzyme is a dimer of subunits (3, 131, having molecular mass of 50,489 Da.Three-dimensional structural studies to date have focused mainly on the plant ribulose-1,5-bisphosphate carboxylase/ oxygenases.Combined electron microscopy and x-ray diffraction have established that ribulose-1,5-bisphosphate carboxylase/oxygenase from tobacco has an LSSs structure, where L represents the large subunit and S represents the small sub-