Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 365, Issue 5, Pages 1429-1445Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2006.10.061
Keywords
phosphorylase kinase; allostery; phosphorylation; subunit interactions; protein-protein interactions
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Funding
- NIDDK NIH HHS [R56 DK032953, R01 DK032953, DK 32953] Funding Source: Medline
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Phosphorylase kinase (PhK), an (alpha beta gamma delta)(4) complex, regulates glycogenolysis. Its activity, catalyzed by the gamma subunit, is tightly controlled by phosphorylation and activators acting through allosteric sites on its regulatory alpha, beta and delta subunits. Activation by phosphorylation is predominantly mediated by the regulatory beta subunit, which undergoes a conformational change that is structurally linked with they subunit and that is characterized by the ability of a short chemical crosslinker to form beta-beta dimers. To determine potential regions of interaction of the beta and gamma subunits, we have used chemical crosslinking and two-hybrid screening. The beta and gamma subunits were crosslinked to each other in phosphorylated PhK, and crosslinked peptides from digests were identified by Fourier transform mass spectrometry, beginning with a search engine developed in house that generates a hypothetical list of crosslinked peptides. A conjugate between beta and gamma that was verified by MS/MS corresponded to crosslinking between K303 in the C-terminal regulatory domain of gamma (gamma CRD) and R18 in the N-terminal regulatory region of beta (beta 1-31), which contains the phosphorylatable serines 11 and 26. A synthetic peptide corresponding to residues 1-22 of beta inhibited the crosslinking between beta and gamma, and was itself crosslinked to K303 of gamma. In two-hybrid screening, the beta 1-31 region controlled beta subunit self-interactions, in that they were favored by truncation of this region or by mutation of the phosphorylatable serines 11 and 26, thus providing structural evidence for a phosphorylation-dependent subunit communication network in the PhK complex involving at least these two regulatory regions of the beta and gamma subunits. The sum of our results considered together with previous findings implicates the gamma CRD as being an allosteric activation switch in PhK that interacts with all three of the enzyme's regulatory subunits and is proximal to the active site cleft. (c) 2006 Elsevier Ltd. All rights reserved.
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