Proximal regions of the catalytic γ and regulatory β subunits on the interior lobe face of phosphorylase kinase are structurally coupled to each other and with enzyme activation

• Published in: Journal of molecular biology Vol. 265; no. 3; pp. 319 - 329
• Main Authors: Wilkinson, Deborah A, Norcum, Mona T, Fizgerald, Thomas J, Marion, Tony N, Tillman, David M, Carlson, Gerald M
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 24.01.1997
• Subjects: activation; Amino Acid Sequence; Animals; Antibodies, Monoclonal - metabolism; Base Sequence; Binding Sites; Coenzymes - metabolism; Enzyme Activation; Enzyme-Linked Immunosorbent Assay; Epitopes - chemistry; Epitopes - immunology; Epitopes - metabolism; Female; immunoelectron microscopy; Microscopy, Immunoelectron - methods; Models, Molecular; Molecular Sequence Data; phosphorylase kinase; Phosphorylase Kinase - chemistry; Phosphorylase Kinase - immunology; Phosphorylase Kinase - metabolism; Protein Conformation; Rabbits; β regulatory subunit; γ catalytic subunit; β regulatory subunit; γT; immunoelectron microscopy; Fab; IgG; mAb; CDR; DHFR; IEM; BSA; γ catalytic subunit; Fab′-SH; γ trnc; phosphorylase kinase; activation; F(ab)′ 2; protein kinase A; ELISA
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1006/jmbi.1996.0739

Phosphorylase kinase from skeletal muscle is a hexadecameric enzyme with the subunit composition (αβγδ) 4 and a mass of 1.3 × 10 6Da. The catalytic γ subunit and the remaining regulatory subunits are packed as a tetrahedral structure composed of two elongated, opposing (αβγδ) 2 octameric lobes. We show by immunoelectron microscopy with subunit-specific monoclonal antibodies that a portion of the β subunit occurs on the interior face of the lobes at a region of inter-lobal interactions, and that at a proximal position slightly more central and distal on the interior lobe face lies the base (residues 277 to 290) of the helical domain of the catalytic core of the γ subunit. Activation of the kinase by a variety of means caused similar increases in the binding to the holoenzyme of the monoclonal antibodies against these two regions of the β and γ subunits. Moreover, monovalent fragments of the antibodies against both regions stimulated the activity of the non-activated holoenzyme. Thus, the epitopes of the β and γ subunits recognized by the monoclonal antibodies are structurally coupled to each other and with the activation of phosphorylase kinase. Activation of the holoenzyme apparently involves the repositioning of the base of the catalytic domain of the γ subunit and a proximal region of the β subunit within the identified area on the interior face of the lobes of the tetrahedral phosphorylase kinase molecule.