InterPro domain: IPR038052

The RbcX protein has been identified as having a chaperonin-like function as it assists in the correct assembly of RbcL and RbcS subunits during RuBisCO biogenesis and it is also required to reach its maximal activity [ 1 , 2 ]. The rbcX gene is juxtaposed to and cotranscribed with rbcL and rbcS encoding RubisCO in Anabaena sp. (strain CA / ATCC 33047) [ 3 ]. Crystal structure studies revealed that RbcX is composed almost exclusively of alpha-helices, which form an unusual four-helix bundle. Additionally, all known RbcX proteins exist as homodimers (RbcX2). The central cleft of this homodimer binds the C-terminal of a RbcL monomer, stabilizing it, and the peripheral region of RbcX2 binds a second RbcL monomer, which allows the RbcL homodimers to be in the correct orientation [ 4 ].

RbcX forms a homodimer with two cooperating RbcL-binding regions [ 5 ]. It is composed of five helices per subunit with irregular array of short and long helices, it also has an unusually long protruding C-terminal helix [ 6 ].

1. Evolution of cyanobacteria by exchange of genetic material among phyletically related strains. J. Bacteriol. 180, 3453-61
2. Initial characteristics of RbcX proteins from Arabidopsis thaliana. Plant Mol Biol 77, 447-59
3. Maximum activity of recombinant ribulose 1,5-bisphosphate carboxylase/oxygenase of Anabaena sp. strain CA requires the product of the rbcX gene. J. Bacteriol. 179, 3793-6
4. Structure of the RuBisCO chaperone RbcX from the thermophilic cyanobacterium Thermosynechococcus elongatus. Acta Crystallogr. Sect. F Struct. Biol. Cryst. Commun. 67, 851-7
5. Structure and function of RbcX, an assembly chaperone for hexadecameric Rubisco. Cell 129, 1189-200
6. Structure of the RuBisCO chaperone RbcX from Synechocystis sp. PCC6803. Acta Crystallogr. D Biol. Crystallogr. 63, 1109-12