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PubMed2001

Localization of plectin and other related proteins along the sarcolemma in smooth muscle cells of rat colon.

Plectin is a versatile linker protein which is associated with various types of cytoskeletal components and/or filaments including intermediate filaments. To better understand the functional roles of plectin in smooth muscle cells, we examined the distribution of plectin and other related proteins in rat colon smooth muscles by confocal laser and electron microscopy. The sarcolemma of smooth muscle cells exhibits two ultrastructurally distinct domains, domains associated with dense plaques and caveola-rich domains. Staining with anti-plectin and anti-desmin antibodies showed that plectin was localized along the sarcolemma in an intermittent manner and desmin was distributed in the sarcoplasm and intermittently at the cell periphery where it was codistributed with desmin. Plectin exhibited complementary and non-overlapping distribution to caveolin-1 and dystrophin, components of caveola domains, whereas plectin was codistributed with vinculin, talin and integrin beta1, components of dense plaques. Plectin was also codistributed with beta2-chain laminin but not with beta1-chain laminin. Electron microscopic observations on the sarcolemma revealed close association of intermediate filaments with dense plaques. Correlated confocal and electron microscopy clearly demonstrated that anti-plectin fluorescence corresponded to dense plaques but not to caveola domains in electron microscopic images. These findings indicate that plectin is confined to dense plaques to which desmin intermediate filaments may be anchored in rat colon smooth muscle cells.

Animals↗
PubMed1992

Immunolocalization of the intermediate filament-associated protein plectin at focal contacts and actin stress fibers.

The distribution of plectin in the cytoplasm of Rat1 and glioma C6 cells was examined using a combination of double and triple immunofluorescence microscopy and interference reflection microscopy. In cells examined shortly after subcultivation (less than 48 h), filamentous networks of plectin structures, resembling and partially colocalizing with vimentin filaments, were observed as reported in previous studies. In cells kept attached to the substrate without growth for periods of 72 h to 8 days (stationary cultures), thick fibrillary plectin structures were observed. These structures were located at the end of actin filament bundles and showed co-distribution with adhesion plaques (focal contacts), vinculin, and vimentin. Only relatively large adhesion plaques (dash-like contacts) were decorated by antibodies to plectin, smaller dot-like contacts at the cell edges remained undecorated. Moreover, in stationary Rat1 cells plectin structures were found to be predominantly colocalized with actin stress fibers. However, after treatment of such cells with colcemid, plectin's distribution changed dramatically. The protein was no longer associated with actin structures, but was distributed diffusely throughout the cytoplasm. After a similar treatment with cytochalasin B, plectin's association with stress fibers again was completely abolished, although stress fibers were still present. The association of plectin with focal contact-associated intermediate filaments was demonstrated also by immunogold electron microscopy of quick-frozen, deep-etched replicas of rat embryo fibroblasts. These data confirm previous reports suggesting a relationship between intermediate filaments on the one hand, and actin stress fibers and their associated plasma membrane junctional complexes, on the other. Furthermore, the data establish plectin as a novel component of focal contact complexes and suggest that plectin plays a role as mediator between intermediate filaments and actin filaments.

Actins↗
PubMed2002

Primary longitudinal adhesion structures: plectin-containing precursors of costameres in differentiating human skeletal muscle cells.

Plectin is a high molecular mass protein (ca 530 kDa) that binds actin, intermediate filaments, and microtubules. Mutations of the human plectin gene cause epidermolysis bullosa simplex with muscular dystrophy. In mature human skeletal muscle, plectin is localized between neighboring myofibrils and between myofibrils and the sarcolemma, both at the level of Z-discs. In the present study we have analyzed plectin expression patterns with emphasis on its sarcolemmal localization during human skeletal muscle differentiation in vitro. In myoblasts plectin showed a cytoplasmic intermediate filament-like distribution, whereas in myotubes plectin is also found at the level of the sarcolemma. In particular, in early myotubes a specific plectin isoform colocalizes with the costameric proteins vinculin and beta1D integrin in longitudinally orientated structures which increased in number and longitudinal extension upon further maturation. In mature myotubes processes perpendicular to the parallel system of longitudinal structures became apparent. Subsequent to the occurrence of spontaneous myofibrillar contractions, the number of longitudinal streaks decreased, and plectin and other costameric proteins were found in an orderly cross-striated sarcolemmal lattice overlying myofibrillar Z-discs. Our study demonstrates that plectin is preassembled together with vinculin and beta1D integrin into primary longitudinal adhesion structures. After the occurrence of spontaneous contractions, these structures reorient and mature costameres are assembled.

Cell Differentiation↗
PubMed2003

Plectin tethers desmin intermediate filaments onto subsarcolemmal dense plaques containing dystrophin and vinculin.

Plectin is a versatile cytoskeletal linker protein that preferentially localizes at interfaces between intermediate filaments and the plasma membrane in muscle, epithelial cells, and other tissues. Its deficiency causes muscular dystrophy with epidermolysis bullosa simplex. To better understand the functional roles of plectin beneath the sarcolemma of skeletal muscles and to gain some insights into the underlying mechanism of plectin-deficient muscular dystrophy, we studied in vivo structural and molecular relationships of plectin to subsarcolemmal cytoskeletal components, such as desmin, dystrophin, and vinculin, in rat skeletal muscles. Immunogold electron microscopy revealed that plectin fine threads tethered desmin intermediate filaments onto subsarcolemmal dense plaques overlying Z-lines and I-bands. These dense plaques were found to contain dystrophin and vinculin, and thus may be the structural basis of costameres. The in vivo association of plectin with desmin, (meta-)vinculin, dystrophin, and actin was demonstrated by immunoprecipitation experiments. Treatment of plectin immunoprecipitates with gelsolin reduced actin, dystrophin, and (meta-)vinculin but not desmin, implicating that subsarcolemmal actin could partly mediate the interaction between plectin and dystrophin or (meta-)vinculin. Altogether, our data suggest that plectin, along with desmin intermediate filaments, might serve a vital structural role in the stabilization of the subsarcolemmal cytoskeleton.

Animals↗
PubMed2003

Expression of plectin in muscle fibers with cytoarchitectural abnormalities.

Plectin is a protein belonging to the cytoskeletal anchoring system, concentrated at sites of mechanical stress in different cell types. In normal skeletal muscle, plectin is located at level of Z-discs, sarcolemma, post-synaptic membrane, and intermyofibrillar network. We investigated plectin immunocytochemistry in lobulated fibers, fibers with tubular aggregates, target fibers, central core disease and centronuclear myopathy. Thirty to forty percent of lobulated fibers had patchy increase of plectin immunoreactivity at sarcolemmal level with focal subsarcolemmal increases. Tubular aggregates revealed a low binding for plectin. Ten percent of central cores exhibited faint focal increase of plectin immunoreactivity. Target formations had a normal plectin pattern. In centronuclear myopathy, plectin immunoreactivity was increased around the centrally located nuclei in 8-12% of the fibers, at the sarcolemma of 50% of type 2 fibers, and at the membrane of small vacuoles located peripherally around the central nuclei. We postulate that plectin may play a role in the subsarcolemmal aggregation of mitochondria in the lobulated fibers, and in the central position of nuclei as well as in shape formation, positioning and moving of the vacuoles in centronuclear myopathy.

Adult↗
PubMed2005

Targeted ablation of plectin isoform 1 uncovers role of cytolinker proteins in leukocyte recruitment.

Plectin, a typical cytolinker protein, is essential for skin and skeletal muscle integrity. It stabilizes cells mechanically, regulates cytoskeleton dynamics, and serves as a scaffolding platform for signaling molecules. A variety of isoforms expressed in different tissues and cell types account for this versatility. To uncover the role of plectin 1, the major isoform expressed in tissues of mesenchymal origin, against the background of all other variants, we raised plectin isoform 1-specific antibodies and generated isoform-deficient mice. In contrast to plectin-null mice (lacking all plectin isoforms), which die shortly after birth because of severe skin blistering, plectin isoform 1-deficient mice were viable at birth, had a normal lifespan, and did not display the skin blistering phenotype. However, dermal fibroblasts isolated from plectin 1-deficient mice exhibited abnormalities in their actin cytoskeleton and impaired migration potential. Similarly, plectin 1-deficient T cells isolated from nymph nodes showed diminished chemotactic migration in vitro. Most strikingly, in vivo we found that leukocyte infiltration during wound healing was reduced in the mutant mice. These data show a specific role of a cytolinker protein in immune cell motility. Single isoform-deficient mice thus represent a powerful tool to unravel highly specific functions of plectin variants.

Actins↗
PubMed1996

M-phase-specific phosphorylation and structural rearrangement of the cytoplasmic cross-linking protein plectin involve p34cdc2 kinase.

Plectin, a widespread and abundant cytoskeletal cross-linking protein, serves as a target for protein kinases throughout the cell cycle, without any significant variation in overall phosphorylation level. One of the various phosphorylation sites of the molecule was found to be phosphorylated preferentially during mitosis. By in vivo phosphorylation of ectopically expressed plectin domains in stably transfected Chinese hamster ovary cells, this site was mapped to the C-terminal repeat 6 domain of the polypeptide. The same site has been identified as an in vitro target for p34cdc2 kinase. Mitosis-specific phosphorylation of plectin was accompanied by a rearrangement of plectin structures, changing from a filamentous, largely vimentin-associated state in interphase to a diffuse vimentin-independent distribution in mitosis as visualized by immunofluorescence microscopy. Subcellular fractionation studies showed that in interphase cells up to 80% of cellular plectin was found associated with an insoluble cell fraction mostly consisting of intermediate filaments, while during mitosis the majority of plectin (> 75%) became soluble. Furthermore, phosphorylation of purified plectin by p34cdc2 kinase decreased plectin's ability to interact with preassembled vimentin filaments in vitro. Together, our data suggest that a mitosis-specific phosphorylation involving p34cdc2 kinase regulates plectin's cross-linking activities and association with intermediate filaments during the cell cycle.

Amino Acid Sequence↗
PubMed1997

Targeted inactivation of plectin reveals essential function in maintaining the integrity of skin, muscle, and heart cytoarchitecture.

Previous studies suggest that plectin, a versatile cytoskeletal linker protein, has an important role in maintaining the structural integrity of diverse cells and tissues. To establish plectin's function in a living organism, we have disrupted its gene in mice. Plectin (-/-) mice died 2-3 days after birth exhibiting skin blistering caused by degeneration of keratinocytes. Ultrastructurally, hemidesmosomes and desmosomes appeared unaffected. In plectin-deficient mice, however, hemidesmosomes were found to be significantly reduced in number and apparently their mechanical stability was altered. The skin phenotype of these mice was similar to that of patients suffering from epidermolysis bullosa simplex (EBS)-MD, a hereditary skin blistering disease with muscular dystrophy, caused by defects in the plectin gene. In addition, plectin (-/-) mice revealed abnormalities reminiscent of minicore myopathies in skeletal muscle and disintegration of intercalated discs in heart. Our results clearly demonstrate a general role of plectin in the reinforcement of mechanically stressed cells. Plectin (-/-) mice will provide a useful tool for the study of EBS-MD, and possibly other types of plectin-related myopathies involving skeletal and cardiac muscle, in an organism amenable to genetic manipulation.

Animals↗
PubMed2006

Plectin regulates the organization of glial fibrillary acidic protein in Alexander disease.

Alexander disease (AxD) is a rare but fatal neurological disorder caused by mutations in the astrocyte-specific intermediate filament protein glial fibrillary acidic protein (GFAP). Histologically, AxD is characterized by cytoplasmic inclusion bodies called Rosenthal fibers (RFs), which contain GFAP, small heat shock proteins, and other undefined components. Here, we describe the expression of the cytoskeletal linker protein plectin in the AxD brain. RFs displayed positive immunostaining for plectin and GFAP, both of which were increased in the AxD brain. Co-localization, co-immunoprecipitation, and in vitro overlay analyses demonstrated direct interaction of plectin and GFAP. GFAP with the most common AxD mutation, R239C (RC GFAP), mainly formed abnormal aggregates in human primary astrocytes and murine plectin-deficient fibroblasts. Transient transfection of full-length plectin cDNA converted these aggregates to thin filaments, which exhibited diffuse cytoplasmic distribution. Compared to wild-type GFAP expression, RC GFAP expression lowered plectin levels in astrocytoma-derived stable transfectants and plectin-positive fibroblasts. A much higher proportion of total GFAP was found in the Triton X-insoluble fraction of plectin-deficient fibroblasts than in wild-type fibroblasts. Taken together, our results suggest that insufficient amounts of plectin, due to RC GFAP expression, promote GFAP aggregation and RF formation in AxD.

Alexander Disease↗
PubMed1983

Specific in situ phosphorylation of plectin in detergent-resistant cytoskeletons from cultured Chinese hamster ovary cells.

Plectin (Mr = 300,000) was found to be an abundant polypeptide component of Chinese hamster ovary cells accounting for up to 1% of cellular protein. Seventy-five per cent of the plectin were present in cytoskeletons prepared by extraction of attached cells with 0.15% Triton X-100. As shown by immunofluorescence microscopy, plectin's spatial arrangement within these cytoskeletal preparations appeared well preserved, though slightly more filamentous compared to nonextracted cells. Upon in situ incubation of cytoskeletons with [gamma-32P] ATP followed by solubilization and immunoprecipitation, plectin was identified as one of the major phosphoacceptors. A basic phosphorylation of the protein was accomplished by a type I cAMP-independent protein kinase, while a cAMP-dependent protein kinase enhanced its phosphorylation up to 2-fold. Peptide mapping revealed that the two kinases phosphorylated different molecular sites. Peptide maps generated from cytoskeletal plectin phosphorylated in vitro using [gamma-32P]ATP and plectin phosphorylated in vivo using 32Pi were virtually identical demonstrating that the in situ phosphorylation of plectin in preparations of cytoskeletons was specific. Moreover, the specific radioactivity of cytoskeletal plectin was three times higher than that of detergent-extracted plectin, suggesting that phosphorylation is important for the protein's association with the cytoskeleton.

Animals↗
PubMed2005

Identification of the cytolinker protein plectin in neuronal cells - expression of a rodless isoform in neurons of the rat superior cervical ganglion.

Plectin, a large (> 500 kDa) dumbbell-shaped cytolinker protein plays an important role in the organization of the cytoskeletal network and the maintenance of cell integrity in a wide variety of tissues and cell types. Earlier experiments revealed the presence of plectin in the central nervous system, whereas the expression in the peripheral nervous system remained unclear. Our results obtained with reverse transcriptase-PCR (RT-PCR) provide evidence that plectin is expressed in structures of the rat peripheral nervous system. In addition to well-characterized plectin transcripts we were able to reveal novel splicing variants affecting the region coding for the central rod domain. Previous studies report a high, but tissue-specific variability of the N-terminal domain of plectin due to alternatively spliced first coding exons and the optionally spliced small exons 2 alpha and 3 alpha. We demonstrate for the first time, using single-cell RT-PCR and immunocytochemistry, that plectin is expressed in neurons of the rat superior cervical ganglion (SCG). Plectin transcripts of single SCG neurons, starting with exon 1c as the first coding exon, contain the optionally spliced exon 2 alpha but lack exon 31. These data therefore suggest that plectin is expressed in rat SCG neurons as a rodless isoform with the molecular mass of 390 kDa.

Alternative Splicing↗
PubMed2002

Direct binding of plectin to Fer kinase and negative regulation of its catalytic activity.

Plectin is a cyoskeletal linker protein that protects tissues against mechanical stress. We report here that the N-terminal domain of the nonreceptor tyrosine kinase Fer interacts with N-terminal sequences of plectin. Recombinant protein encoded by exon 12-24 of rat plectin bound directly to amino acid 1-329 of murine Fer. Using an antiserum prepared to a recombinant N-terminal fragment of Fer kinase, plectin was coimmunoprecipitated with Fer from cell lysates of cultured mouse fibroblasts. Plectin was shown to partially colocalize with Fer in these cells. Upon transfection of full length Fer cDNA into plectin-negative mouse fibroblasts, hyperphosphorylation of Fer was observed; hyperphosphorylation was strongly reduced when N-terminal Fer deletion mutants were transfected. Immunocomplex kinase assays showed that the activity of Fer kinase transfected into plectin-negative fibroblasts was increased compared to that transfected into wild type cells. We conclude that Fer interacts with plectin and that this interaction may serve to negatively regulate Fer's activity.

Animals↗
PubMed1999

Immunogold EM reveals a close association of plectin and the desmin cytoskeleton in human skeletal muscle.

Plectin is a multifunctional cytoskeletal linker protein with an intermediate filament-binding site and sequence elements with high homology to actin-binding domains. Mutations of the human plectin gene as well as the targeted inactivation of its murine analog cause a generalized blistering skin disorder and muscular dystrophy, thus implying its essential role in cells that are exposed to mechanical stress. In the present study we report the characterization of two new domain-specific plectin antibodies as well as ultrastructural localization of plectin in normal human skeletal muscle. Using immunogold electron microscopy, we localized plectin at three prominent sites: 1) Plectin is found at regularly spaced intervals along the cytoplasmic face of the plasma membrane. 2) It is distinctly localized at filamentous bridges between Z-lines of peripheral myofibrils and the sarcolemma and 3) at structures forming the intermyofibrillar scaffold. At the latter two locations, plectin and desmin were found to colocalize. Our ultrastructural analysis suggests that plectin may have a central role in the structural and functional organization of the intermediate filament cytoskeleton in mature human skeletal muscle.

3T3 Cells↗
PubMed1996

Identification of plectin as a substrate of p34cdc2 kinase and mapping of a single phosphorylation site.

Plectin is an in vitro substrate for various kinases present in cell lysates from mitotic and interphase Chinese hamster ovary cells. Sensitivity of plectin kinase activity to the inhibitor olomoucine, and two-dimensional tryptic peptide mapping of plectin phosphorylated by various kinase preparations suggested that the major plectin kinase activity in mitotic extracts is related to the cell cycle regulator kinase p34cdc2. Bacterial expression of various truncated plectin mutant proteins comprising different domains of the molecule and their phosphorylation by purified p34cdc2kinase revealed that the target site of this kinase resided within plectin's C-terminal globular domain. Among the subdomains of the C-terminal region (six repeats and a short tail sequence), only repeat 6 and the tail were phosphorylated by p34cdc2 kinase. As shown by two-dimensional phosphopeptide mapping, repeat 6, but not the tail, contained a mitosis-specific phosphorylation site targeted by p34cdc2 kinase in intact plectin molecules. By performing site-directed mutagenesis of a potential p34cdc2 recognition sequence motif within the repeat 6 domain, threonine 4542 was identified as the major target for the kinase. Protein kinase A, phosphorylating plectin also within repeat 6, targeted sites that were clearly different from those of p34cdc2 kinase.

Animals↗
PubMed2005

Modeling and experimental validation of the binary complex of the plectin actin-binding domain and the first pair of fibronectin type III (FNIII) domains of the beta4 integrin.

The binding of plectin to the beta4 subunit of the alpha6beta4 integrin is a critical step in the formation of hemidesmosomes. An important interaction between these two proteins occurs between the actin-binding domain (ABD) of plectin and the first pair of fibronectin type III (FNIII) domains and a small part of the connecting segment of beta4. Previously, a few amino acids, critical for this interaction, were identified in both plectin and beta4 and mapped on the crystal structures of the ABD of plectin and the first pair of FNIII domains of beta4. In the present study, we used this biochemical information and protein-protein docking calculations to construct a model of the binary complex between these two protein domains. The top scoring computational model predicts that the calponin-homology 1 (CH1) domain of the ABD associates with the first and the second FNIII domains of beta4. Our mutational analysis of the residues at the proposed interface of both the FNIII and the CH1 domains is in agreement with the suggested interaction model. Computational simulations to predict protein motions suggest that the exact model of FNIII and plectin CH1 interaction might well differ in detail from the suggested model due to the conformational plasticity of the FNIII domains, which might lead to a closely related but different mode of interaction with the plectin-ABD. Furthermore, we show that Ser-1325 in the connecting segment of beta4 appears to be essential for the recruitment of plectin into hemidesmosomes in vivo. This is consistent with the proposed model and previously published mutational data. In conclusion, our data support a model in which the CH1 domain of the plectin-ABD associates with the groove between the two FNIII domains of beta4.

Actins↗
PubMed1983

Occurrence and immunolocalization of plectin in tissues.

Various tissues from rat were examined for the occurrence and cellular localization of plectin, a 300,000-dalton polypeptide component present in intermediate filament-enriched cytoskeletons prepared from cultured cells by treatment with nonionic detergent and high salt solution. The extraction of liver, heart, skeletal muscle, tongue, and urinary bladder with 1% Triton/0.6 M KCl yielded insoluble cell residues that contained polypeptides of Mr 300,000 in variable amounts. These high Mr polypeptide species and a few bands of slightly lower Mr (most likely proteolytic breakdown products) were shown to react with antibodies to rat glioma C6 cell plectin using immunoautoradiography and/or immunoprecipitation. By indirect immunofluorescence microscopy using frozen sections (4 micron) of stomach, kidney, small intestine, liver, uterus, urinary bladder, and heart, antigens reacting with antibodies to plectin were found in fibroblast, endothelial, smooth, skeletal, and cardiac muscle, nerve, and epithelial cells of various types. Depending on the cell type, staining was observed either throughout the cytoplasm, or primarily at the periphery of cells, or in both locations. In hepatocytes, besides granular staining at the cell periphery, conspicuous staining of junctions sealing bile canaliculi was seen. In cardiac muscle strong staining was seen at intercalated disks and, as in skeletal muscle, at Z-lines. In cross sections through smooth muscle, most strikingly of urinary bladder, antibodies to plectin specifically decorated regularly spaced, spot-like structures at the cell periphery. By immunoelectron microscopy using the peroxidase technique, antiplectin-reactive material was found along cell junctions of hepatocytes and was particularly enriched at desmosomal plaques and structures associated with their cytoplasmic surfaces. A specific immunoreaction with desmosomes was also evident in sections through tongue. In cardiac muscle, besides Z-lines, intercalated disks were reactive along almost their entire surface, suggesting that plectin was associated with the fascia adherens, desmosomes, and probably gap junctions. In smooth muscle cells, regularly spaced lateral densities probably representing myofilament attachment sites were immunoreactive with plectin antibodies. The results show that plectin is of widespread occurrence with regard to tissues and cell types. Furthermore, immunolocalization by light and electron microscopy at junctional sites of various cell types and at attachment sites of cytoplasmic filaments in epithelial and muscle cells suggests that plectin possibly plays a universal role in the formation of cell junctions and the anchorage of cytoplasmic filaments.

Animals↗
PubMed2003

Specificity of binding of the plectin actin-binding domain to beta4 integrin.

Plectin is a major component of the cytoskeleton and links the intermediate filament system to hemidesmosomes by binding to the integrin beta4 subunit. Previously, a binding site for beta4 was mapped on the actin-binding domain (ABD) of plectin and binding of beta4 and F-actin to plectin was shown to be mutually exclusive. Here we show that only the ABDs of plectin and dystonin bind to beta4, whereas those of other actin-binding proteins do not. Mutations of the ABD of plectin-1C show that Q131, R138, and N149 are critical for tight binding of the ABD to beta4. These residues form a small cavity, occupied by a well-ordered water molecule in the crystal structure. The beta4 binding pocket partly overlaps with the actin-binding sequence 2 (ABS2), previously shown to be essential for actin binding. Therefore, steric interference may render binding of beta4 and F-actin to plectin mutually exclusive. Finally, we provide evidence indicating that the residues preceding the ABD in plectin-1A and -1C, although unable to mediate binding to beta4 themselves, modulate the binding activity of the ABD for beta4. These studies demonstrate the unique property of the plectin-ABD to bind to both F-actin and beta4, and explain why several other ABD-containing proteins that are expressed in basal keratinocytes are not recruited into hemidesmosomes.

Actins↗
PubMed1999

Unusual 5' transcript complexity of plectin isoforms: novel tissue-specific exons modulate actin binding activity.

Plectin, the most versatile cytolinker identified to date, has essential functions in maintaining the mechanical integrity of skin, skeletal muscle and heart, as indicated by analyses of plectin-deficient mice and humans. Expression of plectin in a vast variety of tissues and cell types, combined with a large number of different binding partners identified at the molecular level, calls for complex mechanisms regulating gene transcription and expression of the protein. To investigate these mechanisms, we analyzed the transcript diversity and genomic organization of the murine plectin gene and found a remarkable complexity of its 5'-end structure. An unusually high number of 14 alternatively spliced exons, 11 of them directly splicing into plectin exon 2, were identified. Analysis of their tissue distribution revealed that expression of a few of them is restricted to tissues such as brain, or skeletal muscle and heart. In addition, we found two short exons tissue-specifically spliced into a highly conserved set of exons encoding the N-terminal actin binding domain (ABD), common to plectin and the superfamily of spectrin/dystrophin-type actin binding proteins. Using recombinant proteins we show that a novel ABD version contained in the muscle-specific isoform of plectin exhibits significantly higher actin binding activity than other splice forms. This fine tuning mechanism based on alternative splicing is likely to optimize the proposed biological role of plectin as a cytolinker opposing intense mechanical forces in tissues like striated muscle.

Actins↗