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

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 CO2-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 carboxylase/oxygenase should aid in learning the structure of the other.