Protein surfaces, phosphorylated

Protein phosphorylation-dephosphorylation is a highly versatile and selective process. Not all proteins are subject to phosphorylation, and of the many hydroxyl groups on a protein s surface, only one or a small subset are targeted. While the most common enzyme function affected is the protein s catalytic efficiency, phosphorylation can also alter the affinity for substrates, location within the cell, or responsiveness to regulation by allosteric ligands. Phosphorylation can increase an enzyme s catalytic efficiency, converting it to its active form in one protein, while phosphorylation of another converts it into an intrinsically inefficient, or inactive, form (Table 9—1). 

The activation of adenylyl cyclase enables it to catalyze the conversion of adenosine triphosphate (ATP) to 3 5 -cyclic adenosine monophosphate (cAMP), which in turn can activate a number of enzymes known as kinases. Each kinase phosphorylates a specific protein or proteins. Such phosphorylation reactions are known to be involved in the opening of some calcium channels as well as in the activation of other enzymes. In this system, the receptor is in the membrane with its binding site on the outer surface. The G protein is totally within the membrane while the adenylyl cyclase is within the membrane but projects into the interior of the cell. The cAMP is generated within the cell (see Rgure 10.4). 

The cAMP-dependent protein kinases phosphorylate specific Ser (Thr) residues on target proteins. Given the availability of serine and threonine residues on the surface of globular proteins, how might a protein... 

Since the emulsifying properties depend on the balance between hydro-phobicity and hydrophilicity at the protein surface, a very high yield of phosphorylation may disrupt this balance. The higher improvement of emulsifying properties of K-casein was due to its original high hydro-phobicity, which diminished after phosphorylation. 

Answer The proposition is invalid. Two cells expressing the same surface receptor for a given hormone may have different complements of target proteins for phosphorylation by protein kinases, resulting in different physiological and biochemical responses in different cells. 

Bsbinska A, Ehrlich YH, Komecki E. Activation of human platelets by protein kinase C antibody rede for surface phosphorylation in homeostasis AmJPhysiol 1996 271 H2134-44... 

Tesarik, J., Moos, J., and Mendoza, C. (1993). Stimulation of protein tyrosine phosphorylation by a progesterone receptor on the cell surface of human sperm. Endocrinol. (55 328-335. 

The monomer has a M, of 97 kDa and it is generally thought that the active form of both phosphorylase a and b is the dimer. In the case of phosphorylase b, in the absence of allosteric effectors the equilibrium lies towards the dimer at accessible protein concentrations. Phosphorylation promotes association to the tetramer by generating surface which becomes the interface of the dimer of dimers.The tetramer of phosphorylase a (and presumably phosphorylase b) is inactive and ligands have only modest effects on the association-dissociation equilibria. 

Scheme 12 Strategy for phosphorylated protein/peptide recognition by chemosensors 37, 38 applying a cross-linking interaction with two phosphate groups on a protein surface...

Most of oncogene products that are protein kinases phosphorylate specific tyrosine residues. Examples of these are src, fps, yes and sea. RSVsrc, which occurs in Rous sarcoma virus, has been the most studied. The gene products of src, fps and yes are peripheral membrane proteins associated with the cytoplasmic surface of the plasmalemma (Fig. 11.5). Both p60 " and p60 possess specific tyrosine kinase activity but with an important functional difference, namely, that p60 " kinase activity is regulated through normal cellular mechanisms and does not transform cells, whereas kinase is readily activated and... 

Metal-chelate affinity chromatography was introduced as a specific method for fractionation of proteins by Porath et al., in 1975. The principle of this type of chromatographic method is that certain amino acid residues, such as histidine, cysteine, lysine, tryptophan, aspartic acid, glutamic acid, or phosphorylated amino acids, which are accessible on the protein surface, can interact through non-bonding lone-pair electron coordination with some metal ions. Metal cations Cu, Ni, ... 

In some ion pumps the role of ATP is simple. As shown in Figure 3.7, when the membrane transport protein is phosphorylated it undergoes a conformational change that opens the transmembrane pore and permits it to transport an ion across the membrane. Before the ion can be released at the membrane surface, the transport protein has to be dephosphorylated. 

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