Metal binding to the dynamic cytoplasmic domain of the cation diffusion facilitator (CDF) protein MamM induces a 'locked-in' configuration

Cation diffusion facilitator (CDF) proteins are a conserved family of transmembrane transporters that ensure cellular homeostasis of divalent transition metal cations. Metal cations bind to CDF protein's cytoplasmic C-terminal domain (CTD), leading to closure from its apo open V-shaped dimer to a tighter packed structure, followed by a conformational change of the transmembrane domain thus enabling transport of the metal cation. By implementing a comprehensive range of biochemical and biophysical methods, we studied the molecular mechanism of metal binding to the magnetotactic bacterial CDF protein MamM CTD. Our results reveal that the CTD is rather dynamic in its apo form, and that two dependent metal binding sites, a single central binding site and two symmetrical, peripheral sites, are available for metal binding. However, only cation binding to the peripheral sites leads to conformational changes that lock the protein in a compact state. Thus, this work reveals how metal binding is regulating the sequential uptakes of metal cations by MamM, and extends our understanding of the complex regulation mechanism of CDF proteins. This article is protected by copyright. All rights reserved

Site-specific vibrational dynamics of the CD3 zeta membrane peptide using heterodyned two-dimensional infrared photon echo spectroscopy

Heterodyned two-dimensional infrared (2D IR) spectroscopy has been used to study the amide I vibrational dynamics of a 27-residue peptide in lipid vesicles that encompasses the transmembrane domain of the T-cell receptor CD3zeta. Using 1-C-13=O-18 isotope labeling, the amide I mode of the 49-Leucine residue was spectroscopically isolated and the homogeneous and inhomogeneous linewidths of this mode were measured by fitting the 2D IR spectrum collected with a photon echo pulse sequence. The pure dephasing and inhomogeneous linewidths are 2 and 32 cm(-1), respectively. The population relaxation time of the amide I band was measured with a transient grating, and it contributes 9 cm-1 to the linewidth. Comparison of the 49-Leucine amide I mode and the amide I band of the entire CD3zeta peptide reveals that the vibrational dynamics are not uniform along the length of the peptide. Possible origins for the large amount of inhomogeneity present at the 49-Leucine site are discussed. (C) 2004 American Institute of Physics

Epidermal progenitors give rise to Merkel cells during embryonic development and adult homeostasis

Lineage-tracing experiments show that the origin of specialized mechanosensory Merkel cells in the skin is epidermal progenitors, not the neural crest