Clamp proteins

Figure 2.39 A DNA clamp protein - a trimer of the protein Proliferating Cell Nuclear Antigen (PCNA). The three different trimer units are shown in different colours (image courtesy of www. wikipedia.org). 

No crystallographic structure is currently available for GPV-type single-shelled dsRNA virus capsids. Two cryo-EM reconstructions have been performed, which reveal much the same architecture as the orthoreovirus core a single layer with turrets at the 5-fold vertices, statistically ordered layers of dsRNA, and a clamping protein at 2-fold axes (Hill et al, 1999 ... 

Chapman and Liljas, Fig. 13. Reovims proteins, (a) The X2 turretprotein (Reinisch 2000). The individual domains are marked, (b) The cr2 clamp protein (Reinisch etal, 2000). The two halves of the main part of the protein have approximate 2-fold symmetry. The view is dovm the symmetry axis, (c) The capsid protein (Olland et at, 2001). 

Clamp-loader (heteropentamer) 297.1 Assembles sliding-clamps, protein trafficking... 

FIG. 17 Schematic illustration of the setup for a tip-dip experiment. First glycerol dialkyl nonitol tetraether lipid (GDNT) monolayers are compressed to the desired surface pressure (measured by a Wilhehny plate system). Subsequently a small patch of the monolayer is clamped by a glass micropipette and the S-layer protein is recrystallized. The lower picture shows the S-layer/GDNT membrane on the tip of the glass micropipette in more detail. The basic circuit for measurement of the electric features of the membrane and the current mediated by a hypothetical ion carrier is shown in the upper part of the schematic drawing. 

It is clearly impossible to give a comprehensive overview of this rapidly expanding field. I have chosen a few experts in their field to discuss one (class of) transport protein(s) in detail. In the first five chapters pumps involved in primary active transport are discussed. These proteins use direct chemical energy, mostly ATP, to drive transport. The next three chapters describe carriers which either transport metabolites passively or by secondary active transport. In the last three chapters channels are described which allow selective passive transport of particular ions. The progress in the latter field would be unthinkable without the development of the patch clamp technique. The combination of this technique with molecular biological approaches has yielded very detailed information of the structure-function relationship of these channels. 

Bustamante JO, Liepers A, Prendergast RA, Hanover JA, Oberliethner H. Patch clamp and atomic force microscopy demonstrate TATA-binding protein (TBP) interactions with the nuclear pore complex. JMembrane Biol 1995 146 X263-X272. 

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