title: Calmodulin adopts an extended conformation when interacting with L-selectin in membranes.
abstract: Calmodulin, an intracellular calcium-binding protein, is thought to regulate ectodomain shedding of many membrane proteins, but the underlying molecular mechanism has remained unclear. Basing on a solution structure of calcium-loaded calmodulin in complex with a L-selectin fragment that contains a portion of its transmembrane domain, Gifford et al. (University of Calgary) recently suggested that calmodulin regulates L-selectin shedding by binding directly to a portion of the L-selectin transmembrane domain in a compact conformation. Using fluorescently labeled calmodulin, we show however that calmodulin adopts a distinctly different and much more extended conformation when it binds to the CLS peptide (i.e. the entire transmembrane and cytoplasmic domains of L-selectin) reconstituted in the phosphatidylcholine liposome with micromolar dissociation constant and in a calcium-independent manner. Calmodulin adopts a similarly extended conformation in a ternary complex with the N-terminal FERM domain of moesin and CLS reconstituted in the phospholipid liposome that mimics the native membrane environment. These results indicate that calmodulin does not bind directly to the transmembrane domain of L-selectin. Understanding the association of calmodulin with L-selectin helps to shed light on the mechanisms underlying regulation of ectodomain shedding.
authors: Aflac Cancer and Blood Disorders Center, Department of Pediatrics, Emory University School of Medicine, Atlanta, Georgia, United States of America.
authors: Wei
authors: W
authors: Deng
authors: John A
authors: JA
authors: Putkey
authors: Renhao
authors: R
authors: Li
mesh_terms: D000595:Amino Acid Sequence; D002147:Calmodulin / Q000737:chemistry* / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D006801:Humans; D019041:L-Selectin / Q000737:chemistry / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D014867:Water / Q000737:chemistry
chemical_list: D002147:Calmodulin; D008081:Liposomes; D008840:Microfilament Proteins; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D014867:Water; D019041:L-Selectin; C071058:moesin; C028694:1-palmitoyl-2-oleoylphosphatidylcholine
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