Asymmetric protein localization

Chia If it is just a timing issue we wouldn t expect the asymmetrical protein localization to be affected. 

To see whether similar defects in asymmetric cell divisions and protein localization can be seen in other cdc2 mutant combinations, we used a stock... 

Schuldt A.J., Adams J.H., Davidson C.M.,Micklem D.R., Haseloff J., Johnston D.S., and Brand A.H. 1998. Miranda mediates asymmetric protein and RNA localization in the developing nervous system. Genes Dev. 12 1847-1857. 

Electrophysiological studies often demonstrate multiple, asymmetric mononeuropathies, usually axonal in type, that cannot be localized to typical sites of entrapment (Keswani et al. 2002). CSF analysis reveals nonspecific abnormalities, such as elevated protein and mild mononuclear pleocytosis. Polymerase chain reaction (PCR) for CMV DNA and nerve or muscle biopsy may provide more specific diagnostic data (Roullet et al. 1994). 

FIG. 1. Localization of key proteins involved in the neuroblast asymmetric cell division. During late interphase a complex of proteins including Insc, Baz (and Pins) are localized to the apical cell cortex. This complex acts to mediate the basal cortical localization of the cell fate determinants Numb (and its partner Pon), Pros (and its partner Miranda) and pros RNA (and its partner Staufen) during mitosis. During interphase, Numb is cytoplasmic and Pros is localized to the apical cortex. 

We have previously shown that a 209 amino acid region (aa288-497, asymmetric localization domain) of Insc is necessary and sufficient for apical cortical localization and for mitotic spindle orientation along the apical-basal axis (Tio et al 1999). In a yeast two-hybrid screen we identified Partner of Inscuteable (Pins), a novel 658aa protein with multiple repeats of the Tetratricopeptide (TPR) motif. Affinity purification experiments using embryonic extracts demonstrate that Pins complexes with Insc in vivo. In vitro protein interaction assays demonstrates that Pins interacts with the Insc asymmetric localization domain (see Yu et al 2000). 

In Fig. 3b, L2 and L4 have substantially different STD values, with L4 showing significantly smaller effect, even though these two protons are equidistant from the P3 proton. This is a simple consequence of the differences in the relaxation rates for these L2 and L4 protons due to differences in their local environments (e.g., in the asymmetric model, the L4-L5 distance is shorter than the L3-L2 distance, and thus L4-L5 protons experience a faster longitudinal relaxation rate than the L4-L5 protons). These observations suggest that caution is needed in quahtative attempts to relate the magnitudes of steady state STDs to spatial proximity of ligand protons to the protein protons. 

Biochemical studies have also suggested an asymmetric orientation of constituents in lipid globule membrane. By comparison of specific activities of enzymes in washed lipid globules and released membrane, Patton and Trams (1971) suggested that the active site of Mg2+-adeno-sine triphosphatase was accessible to substrates on both faces of the membrane and that of 5 -nucleotidase on the outer membrane face. Recent evidence from studies of Concanavalin A inhibition of globule membrane and plasma membrane 5 -nucleotidase support an outer surface localization for the active site of this enzyme (Carraway and Carra-way 1976 Snow et al. 1980). Kobylka and Carraway (1973) observed that exposure of lipid globules to proteolytic enzymes resulted in cleavage of all major membrane-associated proteins. They concluded that... 

Lipids also show asymmetrical distributions between the inner and outer leaflets of the bilayer. In the erythrocyte plasma membrane, most of the phosphatidylethanolamine and phosphatidylserine are in the inner leaflet, whereas the phosphatidylcholine and sphingomyelin are located mainly in the outer leaflet. A similar asymmetry is seen even in artificial liposomes prepared from mixtures of phospholipids. In liposomes containing a mixture of phosphatidylethanolamine and phosphatidylcholine, phosphatidylethanolamine localizes preferentially in the inner leaflet, and phosphatidylcholine in the outer. For the most part, the asymmetrical distributions of lipids probably reflect packing forces determined by the different curvatures of the inner and outer surfaces of the bilayer. By contrast, the disposition of membrane proteins reflects the mechanism of protein synthesis and insertion into the membrane. We return to this topic in chapter 29. 

In Figure 3.2 an arbitrary object, here the set of discrete atoms belonging to the backbone structure of a small protein, is chosen as the fundamental unit of construction. This object is termed the asymmetric unit because, in the completed crystal, no part of this object will be systematically related to any other of its parts by crystallographic properties. That is, it has no inherent symmetry or symmetry elements or, if present, they do not coincide with any symmetry operators of the crystal (i.e., the elements generate only internal or local symmetry). In general, the asymmetric unit is one formula unit of a compound, a molecule, or a protein subunit. It can be a small integral number of these, or it may be a fraction such as j or i if the molecule does posses self-symmetry. The essential property of the asymmetric unit for our purposes is the set of relative x, y, z coordinates of the atoms, which comprise its structure. These are, of course, what we are ultimately interested in. 

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