Zasp52, a Core Z-disc Protein in Drosophila Indirect Flight Muscles, Interacts with α-Actinin via an Extended PDZ Domain.

Kuo An Liao,Nicanor González-Morales,Frieder Schöck,Julie L Kadrmas

doi:10.1371/journal.pgen.1006400

Abstract

Z-discs are organizing centers that establish and maintain myofibril structure and function. Important Z-disc proteins are α-actinin, which cross-links actin thin filaments at the Z-disc and Zasp PDZ domain proteins, which directly interact with α-actinin. Here we investigate the biochemical and genetic nature of this interaction in more detail. Zasp52 is the major Drosophila Zasp PDZ domain protein, and is required for myofibril assembly and maintenance. We show by in vitro biochemistry that the PDZ domain plus a C-terminal extension is the only area of Zasp52 involved in the interaction with α-actinin. In addition, site-directed mutagenesis of 5 amino acid residues in the N-terminal part of the PDZ domain, within the PWGFRL motif, abolish binding to α-actinin, demonstrating the importance of this motif for α-actinin binding. Rescue assays of a novel Zasp52 allele demonstrate the crucial importance of the PDZ domain for Zasp52 function. Flight assays also show that a Zasp52 mutant suppresses the α-actinin mutant phenotype, indicating that both proteins are core structural Z-disc proteins required for optimal Z-disc function.

Highlights

Like most animals, invertebrates have three main types of muscles, body wall, heart, and visceral muscle, but in contrast to vertebrates, all of them are striated
We demonstrate that a conserved motif in the N-terminal part of the Zasp52 PDZ domain is responsible for α-actinin binding and that a C-terminal extension of the PDZ domain is required for optimal α-actinin binding
We show genetically that the Zasp52 α-actinin interaction is required for indirect flight muscle (IFM) function, because the α-actinin heterozygous flight defect is suppressed by removal of one copy of Zasp52

Summary

Introduction

Invertebrates have three main types of muscles, body wall, heart, and visceral muscle, but in contrast to vertebrates, all of them are striated. Proteins of the Zasp PDZ domain family function in maintenance of Z-discs and have been proposed to play an important role in myofibril assembly. They have a unique N-terminal PDZ domain in common containing a conserved PWGFRL motif proposed to be required for α-actinin binding [3]. The first three members (ZASP, ENH, and PDLIM7) are called Enigma family proteins and have one N-terminal PDZ domain and three C-terminal LIM domains [4,5,6,7,8]. Mutations in the human ortholog ZASP result in phenotypes of variable severity from congenital myopathy with fetal lethality to late-onset cardiomyopathy [26, 27]

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Conclusion