Protein dislocation

Vectorial Transport - A Function for Poly-Ubiquitination in Protein Dislocation ... 

Wilkinson BM, Tyson JR, Reid PJ, Stirling CJ (2000) Distinct domains within yeast Sec61p involved in post-translational translocation and protein dislocation. J Biol Chem 275 521-529... 

From these examples, it is evident that protein dislocation is a common pathway used by cells to dispose of misfolded proteins. It is obvious that proteins that are located in the ER lumen have to travel across the ER membrane before they can be degraded by the cytosolic proteasome. The question arises whether retrograde translocation is mediated by the translocon or by a completely different translocation system dedicated to dislocating proteins (reviewed in Kopito 1997). 

Jarosch B, Taxis C, Volkwein C et al. (2002) Protein dislocation from the ER requires polyubiquitination andtheAAA-ATPaseCdc48.JVflfCcKRw(4(2), 134-139. 

The primary site of action is postulated to be the Hpid matrix of cell membranes. The Hpid properties which are said to be altered vary from theory to theory and include enhancing membrane fluidity volume expansion melting of gel phases increasing membrane thickness, surface tension, and lateral surface pressure and encouraging the formation of polar dislocations (10,11). Most theories postulate that changes in the Hpids influence the activities of cmcial membrane proteins such as ion channels. The Hpid theories suffer from an important drawback at clinically used concentrations, the effects of inhalational anesthetics on Hpid bilayers are very small and essentially undetectable (6,12,13). 

The involvement of the 26S proteasome in the degradation of ER proteins was demonstrated by the use of specific inhibitors in mammalian cells (Jensen et al. 1995 Ward et al. 1995) and the investigation of conditional proteasome mutants in yeast (Biederer et al. 1997 Hiller et al. 1996). It is still an open question, how substrate proteins, that have been dislocated from the ER, are targeted to the degrading 26S proteasome. Several observations suggest a localization of 26S proteasomes at the cytosolic side of the ER membrane. Impairing the catalytic activity of the proteasome by specific inhibitors results in the accumulation of ubiquitinated forms of CFTR AF508 in insoluble structures surrounded by ER membranes (Johnston et al. 1998). 

Although affinity capillary electrophoresis (ACE) in its classical mode (one of the reagent is dissolved in a BGE, another is injected) is the most widely used technique in the literature, other capillary electrophoretic methods exist which are even more favorable concerning the information about binding parameters obtainable the Hummel-Dreyer (HD) method, frontal analysis (FA), the vacancy peak (VP) method, and vacancy affinity capillary electrophoresis (VACE) (see, e.g., Refs. 49-57). All the methods need as a precondition that the equilibrium between the reactants (say, protein P, drug D, and complex formed PD) is established rapidly compared to the dislocation of the electropho-retically migrating zones. The experimental setup of the HD and the ACE methods is identical, and so is the setup for the VP and the VACE methods. FA differs from all the other techniques. 

Fig. 23. Section of reeler mutant mouse cerebellum stained with monoclonal antibody 4C11 against the P400 protein. Note stained Purkinje cells in the cortex (CX) and in the central mass of dislocated cells (DP). Bar = 200 jum. Maeda et al. (1989).

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