Talk by Dr. Manajit Hayer-Hartl “Chaperone machineries for the biogenesis and metabolic repair of RuBisCO, the most abundant enzyme in nature”

【Abstract】

Ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is responsible for the fixation of atmospheric CO2 in photosynthesis. It is the most abundant enzyme in nature, owing in part to its low catalytic turnover rate and limited specificity for CO2 versus O2. Thus, RuBisCO has long been a target for reengineering with the goal of increasing crop yields. However, genetic manipulation has been hampered by the failure to express plant RuBisCO in a bacterial host.

The major form of RuBisCO (form I) is hexadecameric, consisting of 8 large (RbcL) and 8 small (RbcS) subunits. In recent years it has become evident that the RuBisCO enzyme requires a tremendous amount of help from chaperones to fold and assemble into the functional holoenzyme. We found that seven chaperones –  the chloroplast chaperonin system Cpn60/Cpn20, RuBisCO accumulation factors 1 and 2 (Raf1 and Raf2, respectively), Ribulose-bisphosphate-carboxylase factor X (RbcX) and the protein bundle-sheath defective-2 (BSD2) – mediate the folding and assembly of Arabidopsis thaliana RuBisCO when co-expressed in E. coli. Our biochemical and structural analysis revealed the role of BSD2 in stabilizing an assembly intermediate of eight RbcL subunits until the RbcS subunits become available. The ability to produce plant RuBisCO recombinantly will facilitate efforts to improve the enzyme through mutagenesis.

To become catalytically active, the newly-assembled RuBisCO must first be carbamylated by a non-substrate CO2 molecule at the active-site lysine and bind a Mg2+ ion as cofactor. Premature binding of the substrate ribulose-1,5-biphosphate (RuBP) results in an inactive complex. Inactivation of RuBisCO also occurs during its multistep catalytic reaction, due to the production of ‘misfire’ products such as XuBP or PDBP. Reactivation is catalyzed by a AAA+ (ATPases Associated with various cellular Activities) protein called RuBisCO activase (Rca). More recently, the discovery of the phosphatase XuBPase, which hydrolyzes the inhibitory sugar phosphate XuBP, demonstrated the importance of a functional cooperation of Rca with specific phosphatases in maintaining RuBisCO activity during photosynthesis.

【Biography】

Manajit Hayer-Hartl (Biosketch)
Independent Group Leader (Principal Investigator)
Department Cellular Biochemistry, Max Planck Institute of Biochemistry, Germany.

Biography:
Born in Singapore. Obtained General Teacher Certificate at the Institute of Education, in 1977, in Singapore. Then joined the University of Stirling, Scotland, U.K. and graduated with BSc. Honours in Chemistry in 1981. Obtained scholarship to continue with a PhD in the Chemistry Department which was submitted at the end of 1984.

Post-doctoral training at several Institutions around the world, including Oxford University (UK); Louise Pasteur Institute (Strasbourg, France); Ludwig Maximillian University (Munich, Germany); Jules Stein Eye Institute (Los Angeles, USA). Research Fellow at Sloan Kettering Institute (New York, U.S.A) from 1991 to 1997, followed by a Group Leader position at the Max Planck Institute of Biochemistry in the Department of Cellular Biochemistry (Munich, Germany). Present position, since 2006, as Independent Research Group Leader (Principal Investigator) within the same Department, and since 2014, W2 Position of the Minerva Program of the Max Planck Society.