Molecular interactions with obscurin are involved in the localization of muscle-specific small ankyrin1 isoforms to subcompartments of the sarcoplasmic reticulum.
We report here on experiments aimed to characterise the molecular basis of the interactions between muscle-specific ankyrin1 isoforms localized on the sarcoplasmic reticulum and obscurin a protein associated with the contractile apparatus. A novel small muscle-specific ankyrin isoform, ank1.9 was identified that, similarly to the known ank1.5 isoform, was able to bind to obscurin in yeast two-hybrid assay and in pull-down experiments. Two distinct binding sites in the C-terminus of obscurin were found to mediate binding with ank1.5 and ank1.9. Interactions between ank1.5 and ank1.9 with recombinant proteins containing one or two of the binding sites of obscurin were confirmed by expressing recombinant proteins in NIH3T3 cells. In cultured myotubes, ank1.5 and ank1.9 colocalized with endogenous obscurin at the M-band region. In contrast with evidence of efficient binding between small ank1 isoforms and obscurin, in vitro interaction studies and transfection experiments in myotubes indicated that small ank1 isoforms do not efficiently interact with titin. Altogether, these results support a role of obscurin in mediating the subcellular localization of small ank1 isoforms in striated muscle cells. Given that the localization of small muscle-specific ank1 isoforms mirrors that of obscurin, we propose that obscurin and small ank1 isoforms may form stable interactions that may be relevant to connect the sarcoplasmic reticulum and the contractile apparatus in skeletal muscle cells.
Armani
Andrea
A
Molecular Medicine Section, Department of Neuroscience, University of Siena, 53100 Siena, Italy.
Galli
Sara
S
Giacomello
Emiliana
E
Bagnato
Paola
P
Barone
Virginia
V
Rossi
Daniela
D
Sorrentino
Vincenzo
V
D000595:Amino Acid Sequence; D000818:Animals; D017487:Ankyrins / Q000235:genetics / Q000378:metabolism*; D064211:Connectin; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism; D041681:NIH 3T3 Cells; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D064067:Rho Guanine Nucleotide Exchange Factors; D016415:Sequence Alignment; D020798:Two-Hybrid System Techniques
C491707:Ank1 protein, mouse; D017487:Ankyrins; D064211:Connectin; D020662:Guanine Nucleotide Exchange Factors; D009124:Muscle Proteins; C503780:Obscn protein, rat; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; D064067:Rho Guanine Nucleotide Exchange Factors; C577285:TTN protein, human; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; C515766:obscn protein, mouse