Selenocysteine incorporation in Kinetoplastid: selenophosphate synthetase (SELD) from Leishmania major and Trypanosoma brucei.

Selenophosphate synthetase (EC 2.7.9.3), the product of the selD gene, produces the biologically active selenium donor compound, monoselenophosphate, from ATP and selenide, for the synthesis of selenocysteine. The kinetoplastid Leishmania major and Trypanosoma brucei selD genes were cloned and the SELD protein overexpressed and purified to apparent homogeneity. The selD gene in L. major and T. brucei are respectively 1197 and 1179 bp long encoding proteins of 399 and 393 amino acids with molecular masses of 42.7 and 43 kDa. The molecular mass of 100 kDa for both (L. major and T. brucei) SELDs is consistent with dimeric proteins. The kinetoplastid selD complement Escherichia coli (WL400) selD deletion confirming it is a functional enzyme and the specific activity of these enzymes was determined. A conserved Cys residue was identified both by multiple sequence alignment as well as by functional complementation and activity assay of the mutant (Cys to Ala) forms of the SELD identifying this residue as essential for the catalytic function.

Crystal structure of human phosphoglucose isomerase and analysis of the initial catalytic steps.

The second enzyme in the glycolytic pathway, phosphoglucose isomerase (PGI), catalyses an intracellular aldose-ketose isomerization. Here we describe the human recombinant PGI structure (hPGI) solved in the absence of active site ligands. Crystals isomorphous to those previously reported were used to collect a 94% complete data set to a limiting resolution of 2.1 A. From the comparison between the free active site hPGI structure and the available human and rabbit PGI (rPGI) structures, a mechanism for protein initial catalytic steps is proposed. Binding of the phosphate moiety of the substrate to two distinct elements of the active site is responsible for driving a series of structural changes resulting in the polarisation of the active site histidine, priming it for the initial ring-opening step of catalysis.

Human phosphoglucose isomerase: expression, purification, crystallization and preliminary crystallographic analysis.

Phosphoglucose isomerase (PGI) is the second enzyme in the glycolytic pathway and catalyzes an aldose-ketose isomerization. Outside the cell, PGI has been found to function as both a cytokine and as a growth factor. The human pgi gene was cloned and the expressed enzyme was purified to homogeneity. Isomorphous crystals were obtained under two conditions and belong to the P2(1)2(1)2(1) space group, with unit-cell parameters a = 80.37, b = 107.54, c = 270.33 A. A 94.7% complete data set was obtained and processed to a limiting resolution of 2.6 A. The asymmetric unit contains two hPGI dimers according to density calculations, a self-rotation function map and molecular-replacement solution.