1smk
Mature and translocatable forms of glyoxysomal malate dehydrogenase have different activities and stabilities but similar crystal structures
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OverviewOverview
Many organelle enzymes coded for by nuclear genes have N-terminal, sequences, which directs them into the organelle (precursor) and are, removed upon import (mature). The experiments described below characterize, the differences between the precursor and mature forms of watermelon, glyoxysomal malate dehydrogenase. Using recombinant protein methods, the, precursor (p-gMDH) and mature (gMDH) forms were purified to homogeneity, using Ni2+-NTA affinity chromatography. Gel filtration and dynamic light, scattering have shown both gMDH and p-gMDH to be dimers in solution with, p-gMDH having a correspondingly higher molecular weight. p-gMDH also, exhibited a smaller translational diffusion coefficient (D(t)) at, temperatures between 4 and 32 degrees C resulting from the extra amino, acids on the N-terminal. Differential scanning calorimetry described, marked differences in the unfolding properties of the two proteins with, p-gMDH showing additional temperature dependent transitions. In addition, some differences were found in the steady state kinetic constants and the, pH dependence of the K(m) for oxaloacetate. Both the organelle-precursor, and the mature form of this glyoxysomal enzyme were crystallized under, identical conditions. The crystal structure of p-gMDH, the first structure, of a cleavable and translocatable protein, was solved to a resolution of, 2.55 A. GMDH is the first glyoxysomal MDH structure and was solved to a, resolution of 2.50 A. A comparison of the two structures shows that there, are few visible tertiary or quaternary structural differences between, corresponding elements of p-gMDH, gMDH and other MDHs. Maps from both the, mature and translocatable proteins lack significant electron density prior, to G44. While no portion of the translocation sequences from either, monomer in the biological dimer was visible, all of the other solution, properties indicated measurable effects of the additional residues at the, N-terminal.
About this StructureAbout this Structure
1SMK is a Single protein structure of sequence from Citrullus lanatus with CIT as ligand. Active as Malate dehydrogenase, with EC number 1.1.1.37 Full crystallographic information is available from OCA.
ReferenceReference
Organelle and translocatable forms of glyoxysomal malate dehydrogenase. The effect of the N-terminal presequence., Cox B, Chit MM, Weaver T, Gietl C, Bailey J, Bell E, Banaszak L, FEBS J. 2005 Feb;272(3):643-54. PMID:15670147
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