A Class III PDZ Binding Motif in the Myotilin and FATZ Families Binds Enigma Family Proteins: a Common Link for Z-Disc Myopathies

Abstract

Interactions between Z-disc proteins regulate muscle functions and disruption of these interactions results in muscle disorders. Mutations in Z-disc components myotilin, ZASP/Cypher, and FATZ-2 (calsarcin-1/ myozenin-2) are associated with myopathies. We report here that the myotilin and the FATZ (calsarcin/ myozenin) families share high homology at their final C-terminal five amino acids. ThisL motif is present almost exclusively in these families and is evolutionary conserved. We show by in vitro and in vivo studies that proteins from the myotilin and FATZ (calsarcin/myozenin) families interact via this novel type of class III PDZ binding motif with the PDZ domains of ZASP/Cypher and other Enigma family members: ALP, CLP-36, and RIL. We show that the interactions can be modulated by phosphorylation. Calmodulin-dependent kinase II phosphorylates the C terminus of FATZ-3 (calsarcin-3/myozenin-3) and myotilin, whereas PKA phosphorylates that of FATZ-1 (calsarcin-2/myozenin-1) and FATZ-2 (calsarcin-1/ myozenin-1). This is the first report of a binding motif common to both the myotilin and the FATZ (calsarcin/ myozenin) families that is specific for interactions with Enigma family members.The sarcomere of striated muscle consists of strictly organized subunits, myosin-containing thick filaments and actincontaining thin filaments. The thin filaments are aligned and cross-linked at the Z-discs by a molecular complex in which ␣-actinin is one of the core structures. Since the contractile force is transduced via the Z-discs, this structure has special requirements. It must provide extensive stability and yet undergo modulation in response to external signals. The Z-discs also serve as important sensors of extracellular cues and mediators of cellular signals that result in various adaptive responses (37). Muscle cells are able to sense changes in their workload and adapt accordingly via complex signaling pathways, some involving calcium, since its level in muscle cells alters in response to nerve pulses and muscle contraction. Of special importance is calcineurin, a sarcomeric calcium/calmodulin-dependent phosphatase that can act as a sensor of change. It is involved in the regulation of genes affecting muscle differentiation and fiber-type specification (12, 13).The special role of the Z-discs is indicated by the fact that mutations in several Z-disc proteins can result in neuromuscular disorders and cardiomyopathies. For instance, myofibrillar myopathy (desmin-related myopathy), a disease characterized by sarcomere disintegration and accumulation of thin filament material, is caused by dominantly inherited missense mutations in Z-disc proteins: myotilin, filamin-C, and Z-band alternatively spliced PDZ motif-containing protein (ZASP, also named LIM domain-binding factor 3, Cypher, or Oracle) (42, 43, 52). Missense mutations in myotilin can also result in limbgirdle muscular dystrophy 1A and spheroid body myositis (10, 18), while mutations in ZASP/Cypher (8, 57), myopalladin or FATZ-2 (calsarcin-1/myozenin-2) have been ...

Characterization of CLP36/Elfin/PDLIM1 in the nervous system

“…This suggests that the protein that binds to the PDZ domain of CLP36 has a critical role in neurite outgrowth. Recently, it has been shown that palladin binds to the PDZ domain of ALP/Enigma family proteins (von Nandelstadh et al 2009). Palladin is an actin cross-linking protein and interacts with Ena/VASP and profilin which regulate actin polymerization (Goicoechea et al 2008).…”

“…It has been shown that ALP/Enigma proteins interact with ABPs such as aactinin (Xia et al 1997;Zhou et al 1999;Nakagawa et al 2000;Torrado et al 2004;Vallenius et al 2004), b-tropomyosin (Guy et al 1999), and palladin (von Nandelstadh et al 2009), and through these interactions ALP/Enigma proteins are thought to participate in the organization and regulation of cytoarchitecture. The members of this family has one amino-terminal PDZ domain and one carboxyterminal LIM domain [CLP36, Mystique, ALP, and Reversion-induced LIM protein (RIL)] or a single amino-terminal PDZ domain and three carboxy-terminal LIM domains [enigma homologue protein (ENH), ZASP/Cypher, Enigma].…”

Cardiac Z-disc Signaling Network

“…Again, at least five of the 10 known PDZ-LIM pro-teins localize to the z-disc (including Enigma, ENH, Cypher/ ZASP/Oracle, CLP36, and ALP). Recently, van Nandelstadh et al (16) proposed a new PDZ type III domain in proteins of the myotilin family (including myotilin, palladin, and myopalladin) and the calsarcin/FATZ/myozenin family that mediates the interaction of both families with proteins of the Enigma family.…”

Myofibrillar Myopathies and the Z-Disk Associated Proteins

“…The serine rich domain consists of a stretch of hydrophobic residues that are believed to direct the localisation of Myotilin to the sarcolemma [10]. The serine rich domain is also responsible for the interaction of Myotilin with a range of proteins including the primary Z-disk crosslinker -Actinin [153], Filamin-Actin-and Telethonin-binding protein of the Z-disk (FATZ, Myozenin, Calsarcin) [157], ZASP/Cypher [158], Filamin C [157,159] and the ubiquitin ligases MURF-1 and MURF-2 [160]. Interaction of Myotilin with FATZ directly or indirectly directs the localisation of FATZ to the Z-disk [157].…”

“…ZASP contains a PDZ domain, located at the N-terminus, and an internal ZASP/cypher-like motif (ZM) both capable of interacting with -Actinin-2 [179][180][181]. Additionally, the PDZ domain interacts with Myotilin [158] and FATZ [182], which provides structural stability to the Z-disk. The Cterminus contains three LIM domains, which act to recruit signalling proteins to the Z-disk.…”