A Ligand Peptide Motif Selected from a Cancer Patient Is a Receptor-Interacting Site within Human Interleukin-11

Interleukin-11 (IL-11) is a pleiotropic cytokine approved by the FDA against chemotherapy-induced thrombocytopenia. From a combinatorial selection in a cancer patient, we isolated an IL-11-like peptide mapping to domain I of the IL-11 (sequence CGRRAGGSC). Although this motif has ligand attributes, it is not within the previously characterized interacting sites. Here we design and validate in-tandem binding assays, site-directed mutagenesis and NMR spectroscopy to show (i) the peptide mimics a receptor-binding site within IL-11, (ii) the binding of CGRRAGGSC to the IL-11Rα is functionally relevant, (iii) Arg4 and Ser8 are the key residues mediating the interaction, and (iv) the IL-11-like motif induces cell proliferation through STAT3 activation. These structural and functional results uncover an as yet unrecognized receptor-binding site in human IL-11. Given that IL-11Rα has been proposed as a target in human cancer, our results provide clues for the rational design of targeted drugs

A likelihood ratio test for evolutionary rate shifts and functional divergence among proteins

Changes in protein function can lead to changes in the selection acting on specific residues. This can often be detected as evolutionary rate changes at the sites in question. A maximum-likelihood method for detecting evolutionary rate shifts at specific protein positions is presented. The method determines significance values of the rate differences to give a sound statistical foundation for the conclusions drawn from the analyses. A statistical test for detecting slowly evolving sites is also described. The methods are applied to a set of Myc proteins for the identification of both conserved sites and those with changing evolutionary rates. Those positions with conserved and changing rates are related to the structures and functions of their proteins. The results are compared with an earlier Bayesian method, thereby highlighting the advantages of the new likelihood ratio tests

Barttin modulates trafficking and function of ClC-K channels

Barttin is an accessory subunit of a subgroup of ClC-type chloride channels expressed in renal and inner ear epithelia. In this study, we examined the effects of barttin on two ClC-K channel isoforms, rat ClC-K1 and human ClC-Kb, using heterologous expression, patch clamping, confocal imaging, and flow cytometry. In the absence of barttin, only a small percentage of rClC-K1 and hClC-Kb channels are inserted into the plasma membrane. Coexpression of barttin enhances surface membrane insertion and furthermore modifies permeation and gating of ClC-K channels. hClC-Kb channels are nonfunctional without barttin and require the coexpressed accessory subunit to become anion conducting. In contrast, rClC-K1 channels are active without barttin, but at the cost of reduced unitary conductance as well as altered voltage dependence of activation. We mapped the separate functions of barttin to structural domains by a deletion analysis. Whereas the transmembrane core is necessary and sufficient to promote ClC-K channel exit from the endoplasmic reticulum, a short cytoplasmic segment following the second transmembrane helix modifies the unitary conductance. The entire cytoplasmic carboxyl terminus affects the open probability of ClC-K channels. The multiple functions of barttin might be necessary for a tight adjustment of epithelial Cl(−) conductances to ensure a precise regulation of body salt content and endocochlear potential