Phosphoenolpyruvate carboxylase: Difference between revisions
No edit summary |
No edit summary |
||
| Line 19: | Line 19: | ||
== PEPC enzyme structure == | == PEPC enzyme structure == | ||
Overall, plant PEPC’s present a similar structure characterized by four 105-110kDa identical subunits with a conserved N-terminal serine-phosphorylation domain, forming homotetramers <ref name="kai2003"/><ref name="O'Leary2011"/>. X-ray crystallography studies on Escherichia coli and maize (Zea mays) PEPC’s show that the tetramer is comprised of two pairs of monomers with a greater amount of intersubunit contacts, suggesting a homotetrameric structure of a ‘‘dimer-of-dimers’’. The monomeric structure maize’s C4-PEPC monomer consists of an eight-stranded β barrel and 42 α helices <ref name="kai2003"/><ref name="Izui2004">PMID: 15725057</ref>. The <scene name='57/573979/Cv/2'>active site</scene> of each monomer, bound to PEP and the <scene name='57/573979/Cv/3'>Mn+2 ion</scene> cofactor, is located in the C-terminus region of the β barrel <ref name="matsumura2002">/. | Overall, plant PEPC’s present a similar structure characterized by four 105-110kDa identical subunits with a conserved N-terminal serine-phosphorylation domain, forming homotetramers <ref name="kai2003"/><ref name="O'Leary2011"/>. X-ray crystallography studies on Escherichia coli and maize (Zea mays) PEPC’s show that the tetramer is comprised of two pairs of monomers with a greater amount of intersubunit contacts, suggesting a homotetrameric structure of a ‘‘dimer-of-dimers’’. The dimers are held together through an interation between Arg-438 of one subunit and Glu-433 of the neighboring subunit, forming a salt bridge <ref>PMID: 9927652</ref>. The monomeric structure maize’s C4-PEPC monomer consists of an eight-stranded β barrel and 42 α helices <ref name="kai2003"/><ref name="Izui2004">PMID: 15725057</ref>. The <scene name='57/573979/Cv/2'>active site</scene> of each monomer, bound to PEP and the <scene name='57/573979/Cv/3'>Mn+2 ion</scene> cofactor, is located in the C-terminus region of the β barrel <ref name="matsumura2002">PMID: 12467579</ref>. | ||
The comparison between closely related C3 and C4 PEPC’s from F. pringlei (C3) and T. trinervia (C4) was very important in determining the changes responsible for the differences in the enzymes activity in C3 and C4 plants. Structural superposition of these two isoforms shows high levels of structural similarity, supported by the low backbone root-mean square deviation of 0.4 Å <ref name="Paulus2013"/>. Two important site-specific differences between the two structures are a substitution of the 884 residue located close to the feedback inhibitor-binding site, and another residue substitution at the 774 position. The first is largely responsible for the drastic differences observed between the inhibitor tolerances of the C3 and C4 PEPC’s, while the second is a key determinant for the different kinetic properties of F. pringlei and T. trinervia PEPC’s <ref name="blasing2000"/><ref name="Paulus2013"/>. | The comparison between closely related C3 and C4 PEPC’s from F. pringlei (C3) and T. trinervia (C4) was very important in determining the changes responsible for the differences in the enzymes activity in C3 and C4 plants. Structural superposition of these two isoforms shows high levels of structural similarity, supported by the low backbone root-mean square deviation of 0.4 Å <ref name="Paulus2013"/>. Two important site-specific differences between the two structures are a substitution of the 884 residue located close to the feedback inhibitor-binding site, and another residue substitution at the 774 position. The first is largely responsible for the drastic differences observed between the inhibitor tolerances of the C3 and C4 PEPC’s, while the second is a key determinant for the different kinetic properties of F. pringlei and T. trinervia PEPC’s <ref name="blasing2000"/><ref name="Paulus2013"/>. | ||