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Biomedical subjects

B M Pearse

Publications and source records attributed to B M Pearse.

36 records · Page 2Linked to original sources
PubMed1985

Assembly of the mannose-6-phosphate receptor into reconstituted clathrin coats.

In ionic conditions in which clathrin coats are stable, the mannose-6-phosphate receptor associates with the 100-kd/50-kd coat complexes purified from bullock brain coated vesicles. These aggregates exist as striking spherical structures of 300-1000 A diameter. When clathrin is included in the assembly mixture, cages are formed which apparently encapsulate these aggregates, giving, in the absence of lipid, structures resembling full coated vesicles.

Animals↗
PubMed1984

Purification and properties of 100-kd proteins from coated vesicles and their reconstitution with clathrin.

Bullock brain coated vesicles contain a family of at least six 100-kd polypeptides which have the property of promoting clathrin assembly. These proteins have been purified from Triton X-100-extracted coated vesicles by a combination of gel filtration and chromatography on hydroxylapatite and DE-52 cellulose. Three major 100-kd species occur as complexes with a stoichiometric amount of a 50-kd polypeptide. On cross-linking these complexes, the chief products appear to contain two polypeptides of 100 kd and two of 50 kd. These 100-kd/50-kd complexes will polymerise with low concentrations of clathrin to give a relatively homogeneous population of coats predominantly of the 'barrel' size. In contrast, three other polypeptides of 100 kd lack the 50-kd protein but polymerise with clathrin under the same conditions to yield coats of a wide range of sizes including 'barrels', truncated icosahedra and particles of greater than 100 nm diameter. When clathrin cages are reassembled with a saturating amount of 100-kd/50-kd complexes and studied by electron microscopy, the additional proteins appear to follow the underlying geometry of the clathrin polyhedra, partially filling in the polygonal faces of the cage structures. Saturation appears to require approximately 3 molecules of 100-kd polypeptide per clathrin trimer.

Animals↗
PubMed1982

Structure of coated pits and vesicles.

Purified coated vesicles typically contain clathrin and auxiliary structural proteins of about 100 000 and 50 000 relative molecular mass (Mr). A model is described for the packing of clathrin trimers into the characteristic pentagons and hexagons of the surface lattices of coats. In a coated vesicle, clathrin appears to bind to an inner 'core' of particles containing the 100 000 and 50 000 Mr proteins. These core proteins may, in turn, bind to receptors in the membrane of the vesicle. The vesicle itself surrounds specific content molecules bound to their respective receptors. Budding coated vesicles are believed to act as molecular filters in cells. The known structural features of coated membranes are discussed in terms of this apparent role.

Animals↗
PubMed1982

Coated vesicles from human placenta carry ferritin, transferrin, and immunoglobulin G.

Coated vesicles prepared by using isotonic gradients retain their contents. Ferritin, transferrin, and immunoglobulin G have been detected in human placental coated vesicles. Triton X-100 extraction of crude coated vesicles removes contaminating uncoated membranes, leaving coated particles and their associated proteins apparently intact; this provides an efficient means of preparing large quantities of coated vesicle proteins. The clathrin cages surround "cores" of structural protein containing polypeptides of 100,000 and 50,000 molecular weight.

Clathrin↗
PubMed1981

Assembly and packing of clathrin into coats.

We present a model for the packing of clathrin molecules into the characteristic hexagons and pentagons covering coated pits and vesicles. The assembly unit is a symmetrical trimer with three extended legs. Polymerization of these units occurs in seconds under suitable conditions, giving empty polyhedral cages resembling the structures around coated vesicles. Images of small, negatively stained fragments of cages, assembled directly on electron microscope grids, reveal details of the structure, which correlate well with the predicted features of the model. There is one clathrin trimer at each polyhedral vertex, and each leg of the trimer extends along two neighboring polyhedral edges. Quasi-equivalent packing in pentagons and hexagons in polyhedra of different sizes requires a variable joint at the vertex of the molecule and a hinge in each leg. The construction of clathrin coats is remarkable for the extended fibrous contacts that each molecule makes with many others. Such contacts may confer mechanical strength combined with flexibility needed when a vesicle is pinched off from the membrane.

Clathrin↗
PubMed1980

Coated pits act as molecular filters.

Two proteins--theta and H63 antigens--are found to be excluded from coated pits on fibroblast plasma membranes. Coated pits thus act as molecular filters, pinching off, into the cell, lipid vesicles containing a limited number of specific receptors but excluding other plasma membrane proteins. This constitutes part of a lipid flow cycle that was proposed earlier to explain the capping of crosslinked surface antigens.

Animals↗
PubMed1976

Clathrin: a unique protein associated with intracellular transfer of membrane by coated vesicles.

Coated vesicles have been purified from brain, adrenal medulla, and a nonsecreting lymphoma cell line. A single major protein species, clathrin, with an apparent molecular weight of 180,000, forms the coat of all these vesicles. Peptide mapping suggests that the amino acid sequence of clathrin is conserved, irrespective of tissue or species studied. Coated vesicles of different sizes are found. The coats are constructed with variable numbers of clathrin subunits, arranged in closed networks of hexagons and pentagons. The amount of clathrin in lymphoma cells suggests that coated vesicles transfer substantial amounts of membrane within cells, not necessarily in association with a secretory process.

Adrenal Medulla↗