Polar, helical rods

All three types of filament are polar helical rods (i.e., they have chemically distinct "heads" and tails ). In addition to the multiple contacts between subunits that serve to stabilize the filaments, additional multiple binding sites are available to bind auxiliary proteins. These auxiliary proteins can regulate the assembly and disassembly of the filaments, link filaments to one another and to other cellular components including membranes, and allow the filaments to participate in energy-dependent movement. 

The poly(L-lysine) formed a-helical rods in the multilayers that are aligned along the scratching direction of the substrate. He applied attenuated total reflection-Fourier transform spectroscopy (ATR-FTIR) using polarized light for the determination of the orientation within the films. 

Figure 11.7. Transient configuration of M2 helices around the open pore, (a) A barrel of a-helical segments, having a pronounced twist, forms in the cytoplasmic leaflet of the bilayer, constricting the pore maximally at the cytoplasmic membrane surface. The bend in the rods is at the same level as for the closed pore, but instead of pointing inward has rotated over to the side, (b) Schematic representation of the most distant three rods. A tentative alignment of the amino acid sequence with the densities suggests that a line of polar residues (serines and threonine see Fig. 11.3) should be facing the open pore. [From Unwin (31).]...

Cellulose derivatives pack as sheet-like structures, for example, cellulose triacetate or butyrate as well as some ethers, e.g., trimethyl cellulose. Regio-selective derivatives of these mentioned esters or ethers placed at C2 and C3 with various other groups at C6 may belong to the same conformation class, that is, their conformation is determined by the substituent at positions 2 and 3. Many cellulose derivatives crystallize as rod-like helices of various kinds, e.g., 3/2,8/5, and these structures are also found in solvent built-in crystals. It should be mentioned that several cases are known where a change in conformation occurs if a polar solvent is built into the interstitial spaces between the polysaccharide chains. The sheet-like cellulose triacetate conformation converts to a rod-like 8/5 helix with nitromethane present. 

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