Location and distribution of the light chains in clathrin trimers

Mouse monoclonal antibodies have been made that are specific for one of the light chains (LC-A) of calf brain clathrin. The determinant they recognize has been mapped by immunoelectron microscopy and shown to lie near the center of a clathrin trimer. Quantitative immunoprecipitation experiments with one of the monoclonal antibodies suggests that, despite the overall 1:2 stoichiometry, the light chain composition of an individual clathrin trimer is nearly random.

Protein organization in clathrin trimers

We have prepared a homogeneous, soluble 8.6S species ("8.6S clathrin") from calf-brain coated vesicles. Crosslinking experiments show that this 8.6S clathrin is composed of three heavy chains (molecular weight 180,000) and three light chains (molecular weights 33,000 and 36,000). Each heavy chain is in close contact with a single light chain, and the light chains appear not to be in contact with each other. Intact 8.6S clathrin can reassemble into cages without participation of additional protein species.

Protein interfaces and intersubunit bonding. The case of tomato bushy stunt virus

An atomic model of the subunit of tomato bushy stunt virus (TBSV) has been constructed to fit an electron density map at 2.9 A resolution. Subunit interfaces show networks of polar residues forming H-bonds and salt bridges. The way in which alternative specific bonding geometries are built into a contact are described.

Tomato bushy stunt virus at 2.9 A resolution

The polypeptide chain of a TBSV subunit folds into two domains, connected by a hinge, and a flexibly-linked N-terminal arm. Sixty of the 180 N-terminal arms inter-digitate in groups of three, in an unexpected mode of protein association. The remaining 120 arms are not uniquely positioned with respect to the rest of the subunit. RNA is also not uniquely fixed to sites on the major domains.

Hexagonal glycoprotein arrays from Sindbis virus membranes

Freeze-etch electron microscopy of Sindbis virus and of glycoprotein arrays derived from Sindbis membranes by nonionic detergent treatment shows that the local geometry of glycoprotein-glycoprotein interaction does not depend on the presence of the nucleocapsid.

The structural organization of DNA packaged within the heads of T4 wild-type, isometric and giant bacteriophages

We present electron microscopic and X-ray diffraction evidence concerning the structural organization of condensed DNA within a series of T4 bacteriophage with the following head morphologies: prolate (wild-type), isometric and giant (with greatly increased axial ratio). In all cases, the DNA helix segments are locally parallel and 27 A apart. For the giant particles, we show that the DNA forms a large coil whose axis is perpendicular to the axis of the phage tail. This evidence, combined with previous results from a series of isometric bacteriophages (Earnshaw and Harrison, 1977), leads to a model for the organization of condensed DNA that may apply to most dsDNA-containing bacteriophages.

DNA arrangement in isometric phage heads

DNA is wound tightly into phage heads in such a way that it tends to form layers concentric with the rigid protein shell. In P22 and wild-type lambda, DNA completely fills the internal volume, with a highly uniform local packing of adjacent segments; in lambda deletion mutants containing less than a full genome, the local packing distance increases correspondingly.

Glycosidase susceptibility: a probe for the distribution of glycoprotein oligosaccharides in Sindbis virus

Intact Sindbis virus and Triton-solubilized viral glycoprotein were treated with alpha-mannosidase and with a preparation of mixed glycosidases from Diplococcus pneumoniae to probe the accesibility of carbohydrate units on the viral surface. The products of glycosidase attack on Triton-solubilized virus showed that mose carbohydrate units of the glycoproteins are good substrates for these enzymes. The relative resistance of most of the viral oligosaccharides in intact virus particles showed that much of the carbohydrate is not accessible to glycosidases, probably because it is not exposed at the viral surface. The only completely accessible carbohydrate units on Sindbis glycoproteins were the type A oligosaccharides of E2. This differential accessibility of Sindbis oligosaccharides is discussed in relation to the organization of the viral surface.

Tomato bushy stunt virus at 5.5-A resolution

The coat of tomato bushy stunt virus is built from protein subunits having rigid domains connected by a flexible hinge. Two states of the hinge are present in the T=3 icosahedral structure. Each subunit has a binding site for RNA on its inner surface.

Sindbis virus glycoproteins form a regular icosahedral surface lattice

Electron micrographs of negatively stained Sindbis virus particles show that the glycoproteins are organized with trimer clustering in a T = 4 icosahedral surface lattice.