2pem
Crystal structure of RbcX in complex with substrate
Structural highlights
FunctionRBCX_SYNP2 An RbcL-specific chaperone. Required for assembly of the RbcL8 core, acting downstream of the major chaperonin (GroEL-GroES). Acts on newly folded RbcL, has a transient dynamic interaction with RbcL and is eventually displaced by RbcS (PubMed:17574029). The central cleft of the RbcX homodimer (RbcX2) binds the C-terminus of an RbcL monomer, stabilizing the C-terminus and probably preventing its reassociation with chaperonin GroEL-ES. At the same time the peripheral region of RbcX2 binds a second RbcL monomer, bridging the RbcL homodimers in the correct orientation. The RbcX2(2)-bound RbcL dimers then assemble into the RbcL8 core (RbcL8-(RbcX2)8). RbcS binding triggers the release of RbcX2 (By similarity). Required for optimal reconstitution of RuBisCO into its RbcL8S8 holoenzyme form upon expression of rbcL-rbcS subunits in E.coli, and probably also in situ. A frameshift mutation that replaces half the protein reduces accumulation of both RbcL and RbcS subunits and halves activity of RuBisCO in situ and in E.coli (PubMed:15564522).[UniProtKB:Q44212][1] [2] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedAfter folding, many proteins must assemble into oligomeric complexes to become biologically active. Here we describe the role of RbcX as an assembly chaperone of ribulose-bisphosphate carboxylase/oxygenase (Rubisco), the enzyme responsible for the fixation of atmospheric carbon dioxide. In cyanobacteria and plants, Rubisco is an approximately 520 kDa complex composed of eight large subunits (RbcL) and eight small subunits (RbcS). We found that cyanobacterial RbcX functions downstream of chaperonin-mediated RbcL folding in promoting the formation of RbcL(8) core complexes. Structural analysis revealed that the 15 kDa RbcX forms a homodimer with two cooperating RbcL-binding regions. A central cleft specifically binds the exposed C-terminal peptide of RbcL subunits, enabling a peripheral surface of RbcX to mediate RbcL(8) assembly. Due to the dynamic nature of these interactions, RbcX is readily displaced from RbcL(8) complexes by RbcS, producing the active enzyme. The strategies employed by RbcX in achieving substrate specificity and efficient product release may be generally relevant in assisted assembly reactions. Structure and function of RbcX, an assembly chaperone for hexadecameric Rubisco.,Saschenbrecker S, Bracher A, Rao KV, Rao BV, Hartl FU, Hayer-Hartl M Cell. 2007 Jun 15;129(6):1189-200. PMID:17574029[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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