PRELIMINARY-X-RAY CRYSTALLOGRAPHIC STUDY OF WILD-TYPE AND MUTANT RIBULOSE-1,5-BISPHOSPHATE CARBOXLYLASE OXYGENASE FROM CHLAMYDOMONAS-REINHARDTII/

Ribulose-1,5-bisphosphate carboxylase/oxygenase is the key enzyme for photosynthesis. The wild-type and mutant (aminoacid substitutions in t he catalytically important loop 6 region) enzymes from Chlamydomonas r einhardtii, a unicellular green alga, were crystallized. Wild-type, si ngle-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 crysta llized in apparently isomorphous forms. Unit-cell determinations have been completed for three of the enzymes. They display orthorhombic sym metry with similar cell parameters: wild type a = 130.4, b = 203.3, c = 208.5 Angstrom; single mutant (V331A) a = 128.0, b = 203.0, c = 207. 0 Angstrom; and double mutant (V331A/T342I) a =130.0, b = 202.1, c = 2 09.7 Angstrom. Crystals of the wild-type and single-mutant (V331A) enz ymes diffracted to similar to 2.8 Angstrom. A small crystal of the dou ble-mutant (V331A/T342I) enzyme diffracted to similar to 6 Angstrom. A partial data set (68% complete) of the wild-type protein has been col lected at room temperature to about 3.5 Angstrom.