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Physicochemical changes in phosphorylase kinase associated with its activation
Author(s) -
Liu Weiya,
Priddy Timothy S.,
Carlson Gerald M.
Publication year - 2008
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.037895.108
Subject(s) - glycogen phosphorylase , chemistry , phosphorylase kinase , kinase , biochemistry , enzyme , microbiology and biotechnology , biophysics , biology
Phosphorylase kinase (PhK) regulates glycogenolysis through its Ca 2+ ‐dependent phosphorylation and activation of glycogen phosphorylase. The activity of PhK increases dramatically as the pH is raised from 6.8 to 8.2 (denoted as ↑pH), but Ca 2+ dependence is retained. Little is known about the structural changes associated with PhK's activation by ↑pH and Ca 2+ , but activation by both mechanisms is mediated through regulatory subunits of the (αβγδ) 4 PhK complex. In this study, changes in the structure of PhK induced by ↑pH and Ca 2+ were investigated using second derivative UV absorption, synchronous fluorescence, circular dichroism spectroscopy, and zeta potential analyses. The joint effects of Ca 2+ and ↑pH on the physicochemical properties of PhK were found to be interdependent, with their effects showing a strong inflection point at pH ∼7.6. Comparing the properties of the conformers of PhK present under the condition where it would be least active (pH 6.8 − Ca 2+ ) versus that where it would be most active (pH 8.2 + Ca 2+ ), the joint activation by ↑pH and Ca 2+ is characterized by a relatively large increase in the content of sheet structure, a decrease in interactions between helix and sheet structures, and a dramatically less negative electrostatic surface charge. A model is presented that accounts for the interdependent activating effects of ↑pH and Ca 2+ in terms of the overall physicochemical properties of the four PhK conformers described herein, and published data corroborating the transitions between these conformers are tabulated.