Identification of a glutathione-S-transferase effector domain for inhibition of jun kinase, by molecular dynamics.

We have recently found that the glutathione-S-transferase pi-isozyme (GST-pi), a cellular detoxification enzyme, potently and selectively inhibits activation of jun protein by its upstream kinase, jun kinase (JNK). This newly identified regulatory activity of GST-pi is strongly inhibited by a group of agents that inhibit its enzymatic activity. Since loss of enzymatic activity in general does not correlate with loss of regulatory activity, it is likely that inhibitor binding induces changes in the structure of one or more domains of GST that block its interaction with JNK. To identify regions of GST that change conformation on the binding of inhibitors, we have performed molecular dynamics calculations on GST-pi to compute its average structure in the presence and absence of the inhibitor, glutathione sulfonate. Superposition of the two average structures reveals that several regions change local structure depending upon whether the inhibitor is bound or not bound. Two of these regions, residues 36-50 and 194-201, are highly exposed. We have synthesized peptides corresponding to these two segments and find that the 194-201 sequence strongly inhibits the ability of GST-pi to block the in vitro phosphorylation of jun by JNK. These results suggest that this region of GST-pi is critical to its functioning as a newly discovered regulator of signal transduction.

Precipitation of serum proteins by polyethylene glycol (PEG) in pretransfusion testing.

Polyethylene glycol (PEG) is used as a potentiator of blood group antigen-antibody interactions. Although PEG is known to precipitate immunoglobulins, we could find no reports of this reagent entrapping red blood cells (RBCs) in irreversible clumps. The patient we describe here had hyperglobulinemia with a reversed albumin:globulin ratio and a diffuse immunoglobulin peak on serum protein electrophoresis. During preparation of serologic tests, a precipitate formed that entrapped the RBCs when PEG was added. Rapid recognition of this phenomenon could prevent delay in the selection of blood for transfusion by substituting PEG-indirect antiglobulin test (IAT) with another technique such as low-ionic-strength solution (LISS)-IAT, and by increasing the number of washes prior to addition of the antiglobulin reagent.

Diffuse large cell lymphoma of B-cell type associated with reactive hemophagocytosis.

Some lymphomas, virtually all phenotypically of the T-cell type, have been associated with the phenomenon of hemophagocytosis. Only two B-cell lymphomas, one T-cell-rich and the other an angiocentric lymphoma, have been observed to exhibit this phenomenon. A case is reported of a diffuse large cell lymphoma of the B-cell type associated with reactive hemophagocytosis. Cytokines or other humoral factors produced by the lymphoma are a possible cause, and their effect is probably systemic. There is some evidence suggesting correlation of hemophagocytosis with tumor aggressiveness.