Search PubMed⌕ Search

Biomedical subjects

L A Pinna

Publications and source records attributed to L A Pinna.

216 records · Page 12Linked to original sources
PubMed1975

Structural requirements for the enzymatic phosphorylation of phosvitin.

Some structural features required for the enzymatic phosphorylation of phosvitin by purified rat liver cytosol phosvitin kinase have been investigated by testing the activity of such an enzyme toward phosphopeptides differing in size and chemical composition, obtained by pronase or acid hydrolysis of phosvitin. The results obtained can be summarized as follows: (a) Phosvitin kinase phosphorylates even fairly simple phosphopeptides (mol.wt 1000-2000) at rates comparable with intact phosvitin. (b) Acetylation of both phosvitin and pronase phosphopeptides completely prevents their phosphorylation indicating that some lysine residues are strictly required for the phosvitin kinase reaction. (c) Accordingly polyphosphorylserine blocks Ser(P)n which are very actively phosphorylated in phosvitin and pronase phosphopeptides, do not undergo any more enzymatic phosphorylation once isolated as such in a form free of other amino acids. (d) The activity of phosvitin kinase toward substrates probably devoid of Ser(P)n blocks suggests that there are not required for the protein kinase reaction. However, they apparently enhance the phosphorylation rate of the peptide substrates, likely by making easier their binding to the enzyme. It is proposed therefore that the peptidic unit able to undergo phosphorylation by rat liver cytosol phosvitin kinase consists of one or more phosphorylserine residues having in their close proximity a lysine residue playing a critical role in the mechanism of transphosphorylation.

Amino Acids↗
PubMedDate not supplied

An exploration of the effects of constraints on the phosphorylation of synthetic protein tyrosine kinase peptide substrates.

We synthesized by classical solution methods three conformational constrained analogues of EDNEYTA, a heptapeptide sequence that represents the common major autophosphorylation site of the protein tyrosine kinases (PTKs) of the Src family. The correlation between the different structural properties induced by the modifications of the native sequence and the propensity of the peptides to act as PTK substrates was examined. The kinetic data obtained indicate that the introduction of the tyrosine-analogue constraints Tic(OH) and MeTyr, which block the ring flexibility, completely prevents the phosphorylation catalysed by the kinases Lyn and Fgr. On the other hand PTKIIB/p38syk can phosphorylate the two derivatives albeit with an efficiency lower than that found with the native sequence. A third derivative contained side chain to side chain cyclization. This analogue, in which the freedom of the phenolic moiety is not altered, can be phosphorylated by all the PTKs tested with kinetic constants comparable to the parent peptide.

Circular Dichroism↗
PubMedDate not supplied

CK2: a protein kinase in need of control.

Protein kinase CK2 is a heterotetrameric alpha2beta2 Ser/Thr protein kinase with some features unusual among the eukaryotic protein kinases: (1) CK2 recognizes phosphoacceptor sites specified by several acidic determinants; (2) CK2 can use both ATP and GTP as phosphoryl donors; and (3) the regulatory properties of CK2 are poorly understood; it is insensitive to any known second messenger and displays high basal activity. To gain insight into CK2 regulation and to understand its unusual properties, site-directed mutagenesis experiments on both subunits and X-ray crystallographic studies of the catalytic alpha-subunit were performed. The noncatalytic beta-subunit has at least three functions: (1) it protects the alpha-subunit against denaturing agents or conditions; (2) it alters the substrate specificity of the alpha-subunit; and (3) it modulates the activity of the enzyme, i.e., depending on the substrate, it increases or decreases the activity of the alpha-subunit. Mutagenesis experiments revealed that an acidic stretch between amino acids 55 and 64 has a down-regulatory and autoinhibitory function. Mutational analysis of the alpha-subunit has revealed a network of unique basic residues that are responsible for the recognition of phosphoacceptor substrates and for down-regulation by the beta-subunit and by polyanionic inhibitors. The resolution of the crystal structure of Zea mays CK2 alpha-subunit has disclosed the structural features that are responsible for high basal activity and for unusual response to nucleotide analogs. The increasing knowledge of CK2 structure-function relationships will allow the design of highly selective inhibitors of this pleiotropic kinase with oncogenic potential.

Amino Acid Sequence↗