Structural characterization of ordered domains in a hydrophobic membrane protein

Abstract

SynopsisA delipidized proteolipid protein fraction was purified from organic solvent extracts of bovine cerebral cortex and studied by means of diffraction, electron microscopic, and ir techniques. Special use was made of an electron diffraction procedure which minimized the electron damage to the biological specimens. The ir spectroscopy of the apoprotein fraction indicated the presence of polypeptides in extended p-conformation, possibly in the antiparallel mode of packing. Electron microscopy of the fraction, negatively stained in organic media, made apparent the presence of both ordered and amorphous material. Only the former, characterized by repeating units of about 40-45 A in diameter and varying length, produced diffraction patterns in the selected area mode exhibiting a highly undistorted lattice. The two-dimensional cell parameters of the protein fraction were a = 4.79 A, b = 7.20 A, and y = 90'. The plane group symmetry, corresponding to the systematic absences, was p Zgg, consistent with the 6-pleated sheet structure of simple polypeptides.

On the crystalline structure of poly(cyclopentane‐ß‐carboxyamine): An electron diffraction study

“…Calculation of the repeat period of the polyamide in different regular conformations shows none of them to be compatible with the 100 or 010 periodicities derived from the electron diffraction data (Table I). The shortest calculated period (7.80 A) corresponding to the all-trans conformation (2] helix) shown in Figure 4, for example, does not fit any of the spacings observed in the HKO diffraction pattern. It is very probable, therefore, that the chains are packed parallel to the 001 direction and normal to the lamellar faces, as is the case in most polymer crystals described in the literature (7,p.233).…”

Molecular motions in a solid–solid transition of sodium dodecylsulphate

“…Electron diffraction patterns of the lamellar crystals were recorded with the help of an Elmiskop-101 electron microscope, at an accelerating potential of 80 k V, according to a procedure previously described (Macchi, 1976: Macchi & Barrantes, 1979. The microscope was fitted with a universal stage and a double-tilt liquid-nitrogen-cooled specimen holder with provisions to monitor and control the * Present address: Membranbiophysik Gruppe.…”

“…The studies were carried out on commercial grade NadodSO4 (melting range 467-469 K), which, after extensive recrystallization on acetic acid, reached a melting point of 469.6 K. Microscopic single crystals for the ED studies were deposited from dilute solutions (50/~g/ml of NadodSO4 in ethyl ether, ethyl alcohol or acetic acid) on carbon-coated, collodionreinforced copper grids. Electron diffraction patterns of the lamellar crystals were recorded with the help of an Elmiskop-101 electron microscope, at an accelerating potential of 80 k V, according to a procedure previously described (Macchi, 1976: Macchi & Barrantes, 1979. The microscope was fitted with a universal stage and a double-tilt liquid-nitrogen-cooled specimen holder with provisions to monitor and control the * Present address: Membranbiophysik Gruppe.…”

“…In the course of an investigation on the structure and properties of intrinsic components of biological membranes (Macchi & Barrantes, 1979), we became interested in the amphiphile molecule sodium dodecylsulphate (NadodSO4), particularly with respect to the influence of hydrophobic polypeptide residues on the molecular motions of its hydrocarbon tails. The object of this communication is to describe a hitherto unreported solid-solid transition of NadodSO,, which we observed and studied by electron diffraction (ED) in the electron microscope.…”