Sunday, October 30, 2005


MOLECULAR BIOLOGY: ON HEDGEHOG PROTEINS: "The progress of organogenesis is governed by patterning processes that have occurred earlier during development and that involve the action of cell-cell signaling pathways, growth factors acting between cells, and transcription factors acting within cells. In general, both body segmentation and brain patterning are essential for conferring a highly organized functional complexity to the body. In both cases, an originally homogeneous group of cells obtains characteristics to give rise to particular structures and functions in a precise spatial and temporal pattern. This produces patterns such as the regular repetition of skeletal elements and the 3-dimensional compartments of brain primordium on which the subsequent complexity of the neuronal network is organized. It is now widely accepted that similar sets of factors are shared by different animal species and also by distinct processes in the course of early patterning of organogenesis. During animal evolution, a 'prepattern' of fundamental organs apparently emerged relatively early."


CELL BIOLOGY: ON THE ORCHESTRATION OF THE MITOTIC SPINDLE: "Before embarking on mitosis, a cell duplicates its chromosomes, producing pairs of 'sister chromatids'. The members of each pair are identical. In what is known as 'prometaphase' of mitosis, these chromatids become tethered to the spindle, such that one member of each pair is attached to a bundle of microtubules emanating from one pole, and the other member is connected to the other pole. 'Kinetochores' are the microtubule landing pads on chromosomes(3). A tug-of-war ensues, driven by the addition or loss of tubulin (that is, microtubule polymerization or depolymerization) at the kinetochores. This tug-of-war results in chromosomes becoming aligned during metaphase of mitosis, such that each sister faces its final destination. Finally, 'anaphase' begins when the glue holding sisters together is dissolved, and they take off towards opposite spindle poles.(2)"

mitotic spindle

CELL BIOLOGY: ON THE ORCHESTRATION OF THE MITOTIC SPINDLE: "Mitotic spindle, a precision machine made from a bipolar array of microtubules that are focused at each end of the spindle by a centrosome or spindle pole body. Microtubules are themselves dynamic polymers that interact with chromosomes in the middle of the spindle and provide tracks to separate them toward the poles. Without the spindle, cell division would be impossible, and subtle defects in its function are likely to be involved with the genomic instability associated with cancer."
Tuesday, October 18, 2005

Biochem. J. (2004) 380, 161-171 - K. Laulagnier and others - Exosome lipid organization

Biochem. J. (2004) 380, 161-171 - K. Laulagnier and others - Exosome lipid organization: "Exosomes are small vesicles secreted from multivesicular bodies, which are able to stimulate the immune system leading to tumour cell eradication. We have analysed lipids of exosomes secreted either upon stimulation from rat mast cells (RBL-2H3 cells), or constitutively from human dendritic cells. As compared with parent cells, exosomes displayed an enrichment in sphingomyelin, but not in cholesterol. Phosphatidylcholine content was decreased, but an enrichment was noted in disaturated molecular species as in phosphatidylethanolamines. Lyso(bis)phosphatidic acid was not enriched in exosomes as compared with cells. Fluorescence anisotropy demonstrated an increase in exosome-membrane rigidity from pH 5 to 7, suggesting their membrane reorganization between the acidic multivesicular body compartment and the neutral outer cell medium. NMR analysis established a bilayer organization of exosome membrane, and ESR studies using 16-doxyl stearic acid demonstrated a higher flip-flop of lipids between the two leaflets as compared with plasma membrane. In addition, the exosome membrane exhibited no asymmetrical distribution of phosphatidylethanolamines. Therefore exosome membrane displays a similar content of the major phospholipids and cholesterol, and is organized as a lipid bilayer with a random distribution of phosphatidylethanolamines. In addition, we observed tight lipid packing at neutral pH and a rapid flip-flop between the two leaflets of exosome membranes. These parameters could be used as a hallmark of exosomes."

energy transduction

Interpretation of the spatial charge displacements in bacteriorhodopsin in terms of structural changes during the photocycle -- D�r et al. 96 (6): 2776 -- Proceedings of the National Academy of Sciences: "Bacteriorhodopsin (bR) is an integral protein in the plasma membrane of Halobacterium salinarum (1). Upon light absorption, bR transports protons across the membrane, converting the photon energy into the energy of a proton electrochemical gradient. bR is a single small protein and is the simplest known active ion pump and biological light energy transducer. Consequently, it is a prototype system for studying the basic steps and rules of biological energy transduction. "
Saturday, October 08, 2005

Mitochondrial Biology Gets A New Chaperone

Source: Journal of Clinical Investigation
Date Posted: 2005-10-07
Web Address:


Mitochondrial complex I deficiency is one of the most common defects in
patients with mitochondrial disease. The deficiency results from a
failure to assemble the enzyme properly, but the nature of the
molecular chaperones that are necessary for this process in mammals
have remained obscure.

In a new study appearing on October 3 in The Journal of Clinical
Investigation, Eric Shoubridge and colleagues McGill University
identify candidate proteins involved in complex I assembly, and show
that one of the candidates, B17.2L, is an assembly factor. The authors identify a null mutation in a patient with a
progressive encephalopathy, and show that the defect can be
functionally complemented by expression of the wild-type cDNA in
patient cells. They also show that an antibody against the B17.2L
protein recognizes a subassembly of complex I in several additional
patients with complex I assembly defects, but not the whole enzyme
complex itself, consistent with a role as a molecular chaperone.

This is the first molecular chaperone to be characterized for mammalian
complex I, and is the first identification of the genetic basis of
disease in a patient with a complex I assembly defect.

In a related commentary, Robert Nussbaum writes, "The research
described here combines clever model organism genomics and
bioinformatics to identify the first mammalian protein required for the
normal assembly of complex I."

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