IDENTIFICATION OF PHOSPHORYLASE KINASE ALPHA SUBUNIT BINDING PARTNERS IN SKELETAL MUSCLE Soleil Archila August 2004 67 Pages Directed by: Nancy A. Rice, Sigrid Jacobshagen, and Claire A. Rinehart Department of Biology Western Kentucky University Phosphorylase kinase (PhK) integrates neural, hormonal, and metabolic signals in skeletal muscle to tightly regulate glycogen breakdown and energy production. Structurally, PhK is among the largest and most complex kinases known with a stoichiometry of (αβγδ)4 and a mass of 1.3x106 Da. The catalytic γ subunit is allosterically controlled through alterations in quaternary structure initiated by the regulatory α, β and δ subunits. In this study we have chosen to examine the largest regulatory subunit, α. In addition to participating in intramolecular interactions within PhK, α is hypothesized to associate extrinsically with skeletal muscle proteins due to its peripheral location in the holoenzyme. To identify potential muscle protein interactors, the C-terminus of α , amino acid residues 1060-1237, was screened against a rabbit skeletal muscle cDNA library via a yeast two-hybrid assay. Interactions were selected by auxotrophic growth of yeast in the absence of leucine and by expression of β-galactosidase activity. Thirtyseven potential positive clones were initially observed. Secondary selections resulted in 13 putative clones being isolated of which 8 were identified as thyroid hormone receptor interacting protein 10 (TRIP10). TRIP10, also known as Cdc42 interacting protein 4 (CIP4), is highly expressed in skeletal muscle and is thought to act as a regulator of the actin cytoskeleton. The remaining 5 clones were identified as tetratricopeptide repeat protein 1 (TPR1). TPR1 is an adaptor protein that functions in a wide array of cellular processes and is considered a highly specific adaptor. The results reported herein are intriguing given that PhK is associated with the sarcoplasmic reticulum in the A-band / actin filament overlap zone and has previously been shown to interact with the thin filament protein nebulin. To our knowledge, this is the first report to identify TRIP10 as a potential sarcomeric protein, and these findings further suggest a role for PhK in muscle assembly and architecture.