Crystal structure of the soluble form of the redox-regulated chloride ion channel protein CLIC4

The structure of CLIC4, a member of the CLIC family of putative intracellular chloride ion channel proteins, has been determined at 1.8 angstrom resolution by X-ray crystallography. The protein is monomeric and it is structurally similar to CLIC1, belonging to the GST fold class. Differences between the structures of CLIC1 and CLIC4 are localized to helix 2 in the glutaredoxin-like N-terminal domain, which has previously been shown to undergo a dramatic structural change in CLIC1 upon oxidation. The structural differences in this region correlate with the sequence differences, where the CLIC1 sequence appears to be atypical of the family. Purified, recombinant, wild-type CLIC4 is shown to bind to artificial lipid bilayers, induce a chloride efflux current when associated with artificial liposomes and produce an ion channel in artificial bilayers with a conductance of 30 pS. Membrane binding is enhanced by oxidation of CLIC4 while no channels were observed via tip-dip electrophysiology in the presence of a reducing agent. Thus, recombinant CLIC4 appears to be able to form a redox-regulated ion channel in the absence of any partner proteins

The intracellular chloride ion channel protein CLIC1 undergoes a redox-controlled structural transition

Most proteins adopt a well defined three-dimensional structure; however, it is increasingly recognized that some proteins can exist with at least two stable conformations. Recently, a class of intracellular chloride ion channel proteins (CLICs) has been shown to exist in both soluble and integral membrane forms. The structure of the soluble form of CLIC1 is typical of a soluble glutathione S-transferase superfamily protein but contains a glutaredoxin-like active site. In this study we show that on oxidation CLIC1 undergoes a reversible transition from a monomeric to a non-covalent dimeric state due to the formation of an intramolecular disulfide bond (Cys-24-Cys-59). We have determined the crystal structure of this oxidized state and show that a major structural transition has occurred, exposing a large hydrophobic surface, which forms the dimer interface. The oxidized CLIC1 dimer maintains its ability to form chloride ion channels in artificial bilayers and vesicles, whereas a reducing environment prevents the formation of ion channels by CLIC1. Mutational studies show that both Cys-24 and Cys-59 are required for channel activity

Morfologia e reprodução de Chondria curvilineata F.S. Collins & Hervey (Rhodomelaceae, Rhodophyta), uma adição à flora brasileira Morphology and reproduction of Chondria curvilineata F.S. Collins & Hervey (Rhodomelaceae, Rhodophyta, an addition to the Brazilian marine flora

O trabalho a espécie Chondria curvilineata é escrita pela primeira vez para o litoral brasileiro a. O material foi coletado no sublitoral da Lagoa da Conceição, Florianópolis, Santa Catarina. É apresentada uma descrição detalhada da morfologia e reprodução, discutindo e comparando as características diagnósticas da referida espécie com as demais espécies descritas para o Brasil e para outras partes do mundo.<br>Here the species Chondria curvilineata is described for the first time to the Brazilian coast. The material was collected in the subtidal region of Lagoa da Conceição, Florianópolis, Santa Catarina. We present a detailed description of the morphology and reproduction, discussing and comparing the diagnostic characteristic