Cyclic interconversion of methionine containing peptide between oxidized and reduced phases monitored by reversed-phase HPLC and ESI-MS/MS

Mild and Selective Mono-Iodination of Unprotected Peptides as Initial Step for the Synthesis of Bioimaging Probes

Chemoselective functionalization of peptides and proteins to selectively introduce residues for detection, capture, or specific derivatization is of high interest to the synthetic community. Here we report a new method for the mild and effective mono-iodination of tyrosine residues in fully unprotected peptides. This method is highly chemoselective and compatible with a wide variety of functional groups. The introduced iodine can subsequently serve as a handle for further functionalization such as introduction of fluorescent dyes and thus be used for chemoselective labeling of isolated peptides.

A PagP fusion protein system for the expression of intrinsically disordered proteins in Escherichia coli

PagP, a beta-barrel membrane protein found in Gram-negative bacteria, expresses robustly in inclusion bodies when its signal sequence is removed. We have developed a new fusion protein expression system based on PagP and demonstrated its utility in the expression of the unstructured N-terminal region of human cardiac troponin I (residues 1-71). A yield of 100mg fusion protein per liter M9 minimal media was obtained. The troponin I fragment was removed from PagP using cyanogen bromide cleavage at methionine residues followed by nickel affinity chromatography. We further demonstrate that optimal cleavage requires complete reduction of methionine residues prior to cyanogen bromide treatment, and this is effectively accomplished using potassium iodide under acidic conditions. The PagP-based fusion protein system is more effective at targeting proteins into inclusion bodies than a commercially available system that uses ketosteroid isomerase; it thus represents an important advance for producing large quantities of unfolded peptides or proteins in Escherichia coli.