Learners and faculty at two major academic medical centers overwhelmingly preferred CBL (guided inquiry) over PBL (open inquiry). Given the dense medical curriculum and need for efficient use of student and faculty time, CBL offers an alternative model to traditional PBL small-group teaching. This study could not assess which method produces better practicing physicians.
The cytokine interleukin la (IL-la) is a critical mediator of the immune and inflammatory responses.A unique determinant of its activity as compared with IL-1f may be its association with the plasma membrane. While the biologic activity of "membrane IL-1" has been extensively reported, the mechanism of membrane binding remains unclear. We report that the N terminus of the 31-kDa IL-la precursor is myristoylated on specific internal lysine residues. Immunoprecipitation of [3HJmyristic acid-radiolabeled human monocyte lysates with IgG antibodies to the 31-kDa IL-la precursor recovered a protein with the physicochemical properties of the IL-la N-terminal propiece (16 kDa, pl 4.45). Glycyl N-myristoylation of this protein is precluded by the absence of a glycine residue at position 2, suggesting that the propiece is myristoylated on e-amino groups of lysine. To determine which lysine(s) are acylated, a series of synthetic peptides containing all lysines found in the IL-la N-terminal propiece were used in an in vitro myristoylation assay containing peptide, myristoyl-CoA, and monocyte lysate as enzyme source. Analysis of the reaction products by reverse-phase HPLC and gas-phase sequencing demonstrated the specific myristoylation of Lys-82 and Lys-83, yielding predominantly monoacylated product. A conserved sequence in the IL-113 propiece was myristoylated with at least 8-fold less efficiency. Acylation of the IL-la precursor by a previously unrecognized lysyl e-amino N-myristoyltransferase activity may facilitate its specific membrane targeting. N-myristoylation of newly translated proteins has received significant attention as a major determinant of protein targeting and function (for review, see ref. 1). A variety of viral and mammalian membrane-associated proteins are myristoylated; when mutated to nonmyristoylated forms these become soluble, cytosolic proteins with significantly altered function (2-8). For most of these proteins, cotranslational acylation is performed by the enzyme myristoyl CoA:protein N-myristoyltransferase, which forms an amide bond between myristic acid and an N-terminal glycine residue. However, a few myristoylated proteins, including the insulin receptor, the ,u immunoglobulin heavy chain, tumor necrosis factor a, and the interleukin la and 1(3 (IL-la and IL-113) precursors, lack glycine residues correctly positioned for N-myristoylation (9-12). An alternative mechanism for myristoylation of these proteins would be the acylation of internal lysine residues, in which the free E-amino groups form the characteristic amide bonds. While an enzymatically catalyzed fatty acid (octanoyl) acylation of internal lysine E-amino groups has been documented for Agistrodon phospholipase A2 (13), discrete cotranslational myristoylation of internal lysine residues has not been demonstrated.IL-la and IL-1p8 are cytokines with important roles in inflammation and the immune response. Both IL-la and IL-1X3 are translated as 31-to 33-kDa precursors which are subsequently proteolytically processed to the e...
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