Phosphoproteins stability

Espina, V. Phosphoprotein stability in clinical tissue and its relevance for reverse phase protein microarray technology... 

Espina V, Edmiston KH, Heiby M et al (2008) A portrait of tissue phosphoprotein stability in the clinical tissue procurement process. Mol Cell Proteomics 7 1998-2018... 

N-Myristoylation is achieved by the covalent attachment of the 14-carbon saturated myristic acid (C14 0) to the N-terminal glycine residue of various proteins with formation of an irreversible amide bond (Table l). 10 This process is cotranslational and is catalyzed by a monomeric enzyme called jV-myri s toy 11ransferase. 24 Several proteins of diverse families, including tyrosine kinases of the Src family, the alanine-rich C kinase substrate (MARKS), the HIV Nef phosphoprotein, and the a-subunit of heterotrimeric G protein, carry a myr-istoylated N-terminal glycine residue which in some cases is in close proximity to a site that can be S-acylated with a fatty acid. Functional studies of these proteins have shown an important structural role for the myristoyl chain not only in terms of enhanced membrane affinity of the proteins, but also of stabilization of their three-dimensional structure in the cytosolic form. Once exposed, the myristoyl chain promotes membrane association of the protein. 5 The myristoyl moiety however, is not sufficiently hydrophobic to anchor the protein to the membrane permanently, 25,26 and in vivo this interaction is further modulated by a variety of switches that operate through covalent or noncovalent modifications of the protein. 4,5,27 In MARKS, for example, multiple phosphorylation of a positively charged domain moves the protein back to the cytosolic compartment due to the mutated electrostatic properties of the protein, a so-called myristoyl-electrostatic switch. 28 ... 

The stability of the acid-stable phosphoenzyme depends on the presence of both, calcium and magnesium ions in the medium. When the formation of the phosphoenzyme is blocked by removal of calcium ions the intermediate rapidly decays. In contrast, the removal of both ions produces only a partial decay which, however, becomes accelerated on readdition of magnesium ions. These results support the view that magnesium ions are involved in the activation of phosphoprotein decomposition when the pump works in its forward running mode178). 

While it might appear that the phosphoprotein obtained in the above labeling experiments confirms the Morton hypothesis, the pH relationships require some explanation, and various other considerations such as the potent inhibitory properties of phosphate at pH 8.0, its poor inhibitory properties at pH 5.0, the extreme thermodynamic stability of the phosphoprotein and other thermodynamic considerations require further demonstration of a phosphoryl enzyme intermediate (116, 119,... 

Irwin N, Chao S, Goritchenko L, Horiuchi A, Greengard P, Nairn AC, Benowitz LI (2002) Nerve growth factor controls GAP-43 mRNA stability via the phosphoprotein ARPP-19. Proc Natl Acad Sci USA 99 12427-12431. 

A second property in common to all phosphoproteins is the great lability of the phosphate groups in dilute alkali, in contrast to the stability of phosphoamino acids in this medium. 

Mendel DB, BodwellJE, Gametchu B, Harrison RW and Munck A (1986) Molybdate-stabilized nonactivated glucocorticoid-receptor complexes contain a 90-kDa non-steroid-binding phosphoprotein that is lost on activation. J Biol Chem 261 3758-3763. 

Myers, J., et al. (1996). A Method for Enhancing the Sensitivity and Stability of Stains-all for Phosphoproteins Separated in Sodium Dodecyl Sulfate-polyacrylamide Gels, Anal. Biochem. 240 300 302. 

The stability of amorphous tricalcium phosphate is reportedly increased by the presence of ATP or certain phosphoproteins such as phosvitin and casein. 

Materials that interact with DNA to enhance its stability and direct its cellular interactions are being sought. The negative charge on DNA, for example, can be reduced by interaction with cationic lipids or cationic polymers. DNA complexes with proteins and phospholipids have been studied. The phosphoprotein p-53 has excited much interest in connection with tumour suppressor genes and apoptosis (Chapter 10). 

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