3tim
THE CRYSTAL STRUCTURE OF THE "OPEN" AND THE "CLOSED" CONFORMATION OF THE FLEXIBLE LOOP OF TRYPANOSOMAL TRIOSEPHOSPHATE ISOMERASE
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OverviewOverview
Triosephosphate isomerase has an important loop near the active site which, can exist in a "closed" and in an "open" conformation. Here we describe, the structural properties of this "flexible" loop observed in two, different structures of trypanosomal triosephosphate isomerase., Trypanosomal triosephosphate isomerase, crystallized in the presence of, 2.4 M ammonium sulfate, packs as an asymmetric dimer of 54,000 Da in the, crystallographic asymmetric unit. Due to different crystal contacts, peptide 167-180 (the flexible loop of subunit-1) is an open conformation, whereas in subunit-2, this peptide (residues 467-480) is in a closed, conformation. In the closed conformation, a hydrogen bond exists between, the tip of the loop and a well-defined sulfate ion which is bound to the, active site of subunit-2. Such an active site sulfate is not present in, subunit-1 due to crystal contacts. When the native (2.4 M ammonium, sulfate) crystals are transferred to a sulfate-free mother liquor, the, flexible loop of subunit-2 adopts the open conformation. From a closed, starting model, this open conformation was discovered through molecular, dynamics refinement without manual intervention, despite involving C alpha, shifts of up to 7 A. The tip of the loop, residues 472, 473, 474, and 475, moves as a rigid body. Our analysis shows that in this crystal form the, flexible loop of subunit-2 faces a solvent channel. Therefore the open and, the closed conformations of this flexible loop are virtually unaffected by, crystal contacts. The actual observed conformation depends only on the, absence or presence of a suitable ligand in the active site.
About this StructureAbout this Structure
3TIM is a Single protein structure of sequence from Trypanosoma brucei brucei. Active as Triose-phosphate isomerase, with EC number 5.3.1.1 Full crystallographic information is available from OCA.
ReferenceReference
The crystal structure of the "open" and the "closed" conformation of the flexible loop of trypanosomal triosephosphate isomerase., Wierenga RK, Noble ME, Postma JP, Groendijk H, Kalk KH, Hol WG, Opperdoes FR, Proteins. 1991;10(1):33-49. PMID:2062827
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