Preliminary X-ray crystallographic study of wild-type and mutant ribulose-1,5-bisphosphate carboxylase/oxygenase from Chlamydomonas reinhardtii

Ribulose-1,5-bisphosphate carboxylase/oxygenase is the key enzyme for photosynthesis. The wild-type and mutant (amino-acid substitutions in the catalytically important loop 6 region) enzymes from Chlamydomonas reinhardtii, a unicellular green alga, were crystallized. Wild-type, single-mutant (V331A) and two double-mutant (V331A/T342I and V331A/G344S) proteins were activated with cofactors CO₂ and Mg²⁺, complexed with the substrate analog 2'-carboxyarabinitol-1,5-bisphosphate, and crystallized in apparently isomorphous forms. Unit-cell determinations have been completed for three of the enzymes. They display orthorhombic symmetry with similar cell parameters: wild type a = 130.4, b = 203.3, c = 208.5 Å; single mutant (V331A) a = 128.0, b = 203.0, c = 207.0Å; and double mutant (V331A/T342I) a = 130.0, b = 202.1, c = 209.7 Å. Crystals of the wild-type and single-mutant (V331A) enzymes diffracted to 2.8 Å. A small crystal of the double-mutant (V331A/T342I) enzyme diffracted to 6 Å. A partial data set (68% complete) of the wild-type protein has been collected at room temperature to about 3.5 Å.