TY - JOUR
T1 - Versatile architecture of a bacterial aconitase B and its catalytic performance in the sequential reaction coupled with isocitrate dehydrogenase
AU - Tsuchiya, Daisuke
AU - Shimizu, Nobutaka
AU - Tomita, Masaru
PY - 2008/11/1
Y1 - 2008/11/1
N2 - Aconitase B (AcnB) and isocitrate dehydrogenase (ICDH) catalyze the sequential reaction in the Krebs cycle. Since each enzyme was characterized as an independent protein in a diluted condition, the catalytic performance within the cellular metabolism remains unclear. In particular, high macromolecular concentration in the cytosol promotes weak interactions, which affects structure and function of the proteins. We found that the two bacterial enzymes exhibit variable catalytic performance of the sequential reaction, depending on the oligomerization state. The small-angle solution X-ray scattering and the chemical crosslinking analyses revealed that not only the two enzymes but also the fusion protein of the two enzymes assume homodimers in solution. Interestingly, the fusion protein maintains the homodimeric architecture of ICDH, but not AcnB. Instead, one of the two monomeric AcnB regions associates with the homodimeric ICDH region. The fusion protein displayed different catalytic performance of the sequential reaction from that observed in the mixture of the AcnB and ICDH proteins in an equimolar ratio. Connecting the two proteins by a flexible linker yielded a locally high concentration to promote the weak protein-protein interaction. The versatile architecture of AcnB may alter the metabolic process involving the Krebs cycle.
AB - Aconitase B (AcnB) and isocitrate dehydrogenase (ICDH) catalyze the sequential reaction in the Krebs cycle. Since each enzyme was characterized as an independent protein in a diluted condition, the catalytic performance within the cellular metabolism remains unclear. In particular, high macromolecular concentration in the cytosol promotes weak interactions, which affects structure and function of the proteins. We found that the two bacterial enzymes exhibit variable catalytic performance of the sequential reaction, depending on the oligomerization state. The small-angle solution X-ray scattering and the chemical crosslinking analyses revealed that not only the two enzymes but also the fusion protein of the two enzymes assume homodimers in solution. Interestingly, the fusion protein maintains the homodimeric architecture of ICDH, but not AcnB. Instead, one of the two monomeric AcnB regions associates with the homodimeric ICDH region. The fusion protein displayed different catalytic performance of the sequential reaction from that observed in the mixture of the AcnB and ICDH proteins in an equimolar ratio. Connecting the two proteins by a flexible linker yielded a locally high concentration to promote the weak protein-protein interaction. The versatile architecture of AcnB may alter the metabolic process involving the Krebs cycle.
KW - Enzyme catalysis
KW - Krebs cycle
KW - Multienzyme complex
KW - Protein-protein interaction
KW - Quaternary structure of protein
KW - Small-angle solution X-ray scattering
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U2 - 10.1016/j.bbapap.2008.06.014
DO - 10.1016/j.bbapap.2008.06.014
M3 - Article
C2 - 18640291
AN - SCOPUS:54049149716
VL - 1784
SP - 1847
EP - 1856
JO - BBA - Protein Structure
JF - BBA - Protein Structure
SN - 1570-9639
IS - 11
ER -