Rational 'correction' of the amino-acid sequence of RbcX protein from the thermophilic cyanobacterium Thermosynechococcus elongatus dramatically improves crystallization.

RbcX is a dimeric protein found in cyanobacteria that assists in the assembly of the oligomeric RuBisCO complex. RbcX from the thermophile Thermosynechococcus elongatus (TeRbcX) contains an unusual Cys103 residue in its sequence and when expressed recombinantly the protein aggregates and cannot be crystallized. Site-directed mutagenesis of Cys103 to either Arg or Ala produced non-aggregating proteins that could be readily crystallized in several crystal forms. Synchrotron-radiation X-ray diffraction data were collected to 1.96 A resolution and formed the basis of crystal structure analysis of TeRbcX.