MF2120026 Dihydrofolate reductase 1cz3 X-ray 2.10 Homodimer Thermotoga maritima 10731419 Dams T, Auerbach G, Bader G, Jacob U, Ploom T, Huber R, Jaenicke R J. Mol. Biol. 2000 3 297 659-72 Two high-resolution structures have been obtained for dihydrofolate reductase from the hyperthermophilic bacterium Thermotoga maritima in its unliganded state, and in its ternary complex with the cofactor NADPH and the inhibitor, methotrexate. While the overall fold of the hyperthermophilic enzyme is closely similar to monomeric mesophilic dihydrofolate reductase molecules, its quaternary structure is exceptional, in that T. maritima dihydrofolate reductase forms a highly stable homodimer. Here, the molecular reasons for the high intrinsic stability of the enzyme are elaborated and put in context with the available data on the physical parameters governing the folding reaction. The molecule is extremely rigid, even with respect to structural changes during substrate binding and turnover. Subunit cooperativity can be excluded from structural and biochemical data. Major contributions to the high intrinsic stability of the enzyme result from the formation of the dimer. Within the monomer, only subtle stabilizing interactions are detectable, without clear evidence for any of the typical increments of thermal stabilization commonly reported for hyperthermophilic proteins. The docking of the subunits is optimized with respect to high packing density in the dimer interface, additional salt-bridges and beta-sheets. The enzyme does not show significant structural changes upon binding its coenzyme, NADPH, and the inhibitor, methotrexate. The active-site loop, which is known to play an important role in catalysis in mesophilic dihydrofolate reductase molecules, is rearranged, participating in the association of the subunits; it no longer participates in catalysis. GO:0004146 dihydrofolate reductase activity GO:0042802 identical protein binding GO:0050661 NADP binding GO:0005829 cytosol GO:0046452 dihydrofolate metabolic process GO:0046655 folic acid metabolic process GO:0006730 one-carbon metabolic process GO:0046654 tetrahydrofolate biosynthetic process 2 1 Homooligomeric enzymes Homodimeric enzymes All chains according to the most probable oligomerization state stored in PDBe were considered. A Dihydrofolate reductase Thermotoga maritima Q60034 2 165 97% MAKVIFVLAMDVSGKIASSVESWSSFEDRKNFRKITTEIGNVVMGRITFEEIGRPLPERLNVVLTRRPKTSNNPSLVFFNGSPADVVKFLEGKGYERVAVIGGKTVFTEFLREKLVDELFVTVEPYVFGKGIPFFDEFEGYFPLKLLEMRRLNERGTLFLKYSVEKSHR 169 secondary structure helix 24 39 secondary structure helix 45 52 secondary structure helix 81 92 secondary structure helix 102 112 secondary structure strand 2 9 secondary structure strand 14 16 secondary structure strand 40 44 secondary structure strand 59 63 secondary structure strand 75 78 secondary structure strand 96 101 secondary structure strand 117 122 secondary structure strand 125 127 secondary structure strand 131 132 secondary structure strand 140 150 secondary structure strand 157 163 pfam PF00186 Dihydrofolate reductase 5 122 B Dihydrofolate reductase Thermotoga maritima Q60034 2 169 99% MAKVIFVLAMDVSGKIASSVESWSSFEDRKNFRKITTEIGNVVMGRITFEEIGRPLPERLNVVLTRRPKTSNNPSLVFFNGSPADVVKFLEGKGYERVAVIGGKTVFTEFLREKLVDELFVTVEPYVFGKGIPFFDEFEGYFPLKLLEMRRLNERGTLFLKYSVEKSHR 169 secondary structure helix 24 39 secondary structure helix 45 52 secondary structure helix 81 91 secondary structure helix 102 112 secondary structure strand 2 9 secondary structure strand 14 16 secondary structure strand 40 44 secondary structure strand 59 63 secondary structure strand 75 78 secondary structure strand 96 101 secondary structure strand 117 122 secondary structure strand 125 127 secondary structure strand 131 132 secondary structure strand 140 150 secondary structure strand 157 163 pfam PF00186 Dihydrofolate reductase 5 122 Direct evidence The full structure participates in mutual synergistic folding. - The enzyme DHFR from the hyperthermophilic bacterium Thermotoga maritima represents an extremely stable dimer; no isolated structured monomers could be detected in equilibrium or during unfolding. The equilibrium unfolding strictly follows the two-state model for the dimer (PMID:10413491). A N/A B N/A