Taking Aim

Taking Aim. 1993. 41 min., color. video by Monica Frota. For more information contact Monica Frota at Rua Visconde de Ouro Preto 611/201, Rio de Janeiro, Brazil 22250-180, (55 21 5376235).     

Taking two TRAILS

The TNF-related apoptosis-inducing ligand (TRAIL) has well-described anti-inflammatory effects in models of autoimmune disease, including experimental autoimmune encephalomyelitis (EAE). In this issue of Neuron, Aktas, Smorodchenko, and colleagues present evidence that TRAIL exerts anti-inflammatory effects, but also induces neuronal apoptosis, in EAE. This report poses the therapeutic challenge of facilitating TRAIL expression in the periphery while inhibiting TRAIL in the CNS.     

Taking Darwin seriously

Biology &; Philosophy -     

Insulin and insulin mixtures; nph insulin

There are several distinct types of commercial insulins available, and with combinations of these many curves of timing of insulin action may be obtained, but none can parallel the action of a normal pancreas.NPH insulin, the newest addition, has a wide range of usefulness and may supplant many of the other types and combinations.     

Regulation of insulin receptor kinase activity by insulin mimickers and an insulin antagonist

Three agents which mimic insulin action in intact cells (concanavalin A, wheat germ agglutinin, and polyclonal insulin receptor antibody), mimicked insulin's ability to stimulate the kinase activity of purified insulin receptors. In contrast, monoclonal insulin receptor antibody, an antagonist of insulin action, did not stimulate the phosphorylation of the insulin receptor either in intact IM-9 cells or in purified receptor preparations. This antibody, however, antagonized the ability of insulin to stimulate the phosphorylation of the receptor both in intact cells and in the purified receptor. These studies with insulin mimickers and an insulin antagonist are consistent with a role for the kinase activity of the receptor mediating the actions of insulin.     

Engineering of insulin receptor isoform-selective insulin analogues

Background

The insulin receptor (IR) exists in two isoforms, A and B, and the isoform expression pattern is tissue-specific. The C-terminus of the insulin B chain is important for receptor binding and has been shown to contact the IR just adjacent to the region where the A and B isoforms differ. The aim of this study was to investigate the importance of the C-terminus of the B chain in IR isoform binding in order to explore the possibility of engineering tissue-specific/liver-specific insulin analogues.

Methodology/Principal Findings

Insulin analogue libraries were constructed by total amino acid scanning mutagenesis. The relative binding affinities for the A and B isoform of the IR were determined by competition assays using scintillation proximity assay technology. Structural information was obtained by X-ray crystallography. Introduction of B25A or B25N mutations resulted in analogues with a 2-fold preference for the B compared to the A isoform, whereas the opposite was observed with a B25Y substitution. An acidic amino acid residue at position B27 caused an additional 2-fold selective increase in affinity for the receptor B isoform for analogues bearing a B25N mutation. Furthermore, the combination of B25H with either B27D or B27E also resulted in B isoform-preferential analogues (2-fold preference) even though the corresponding single mutation analogues displayed no differences in relative isoform binding affinity.

Conclusions/Significance

We have discovered a new class of IR isoform-selective insulin analogues with 2–4-fold differences in relative binding affinities for either the A or the B isoform of the IR compared to human insulin. Our results demonstrate that a mutation at position B25 alone or in combination with a mutation at position B27 in the insulin molecule confers IR isoform selectivity. Isoform-preferential analogues may provide new opportunities for developing insulin analogues with improved clinical benefits.