Obscurin regulates ankyrin macromolecular complex formation

• Published in: Journal of molecular and cellular cardiology Vol. 168; pp. 44 - 57
• Main Authors: Subramaniam, Janani, Yamankurt, Gokay, Cunha, Shane R.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.07.2022
• Subjects: Alternative splicing; AnkG107; Ankyrin; Ankyrins - chemistry; Muscle Proteins - metabolism; Obscurin; Protein Isoforms - metabolism; Protein Serine-Threonine Kinases; Rho Guanine Nucleotide Exchange Factors - genetics; sAnk1.5; AnkG107; Alternative splicing; Ankyrin; sAnk1.5; Obscurin
• ISSN: 0022-2828; 1095-8584
• DOI: 10.1016/j.yjmcc.2022.04.008

Obscurin is a large scaffolding protein in striated muscle that maintains sarcolemmal integrity and aligns the sarcoplasmic reticulum with the underlying contractile machinery. Ankyrins are a family of adaptor proteins with some isoforms that interact with obscurin. Previous studies have examined obscurin interacting with individual ankyrins. In this study, we demonstrate that two different ankyrins interact with obscurin's carboxyl terminus via independent ankyrin-binding domains (ABDs). Using in-vitro binding assays, co-precipitation assays, and FLIM-FRET analysis, we show that obscurin interacts with small ankyrin 1.5 (sAnk1.5) and the muscle-specific ankyrin-G isoform (AnkG107). While there is no direct interaction between sAnk1.5 and AnkG107, obscurin connects the two ankyrins both in vitro and in cells. Moreover, AnkG107 recruits β-spectrin to this macromolecular protein complex and mutating obscurin's ABDs disrupts complex formation. To further characterize AnkG107 interaction with obscurin, we measure obscurin-binding to different AnkG107 isoforms expressed in the heart and find that the first obscurin-binding domain in AnkG107 principally mediates this interaction. We also find that AnkG107 does not bind to filamin-C and displays minimal binding to plectin-1 compared to obscurin. Finally, both sAnk1.5-GFP and AnkG107-CTD-RFP are targeted to the M-lines of ventricular cardiomyocytes and mutating their obscurin-binding domains disrupts the M-line localization of these ankyrin constructs. Altogether, these findings support a model in which obscurin can interact via independent binding domains with two different ankyrin protein complexes to target them to the sarcomeric M-line of ventricular cardiomyocytes. [Display omitted] •AnkG107 and sAnk1.5 bind obscurin via independent binding sites.•Obscurin forms a complex with AnkG107 and sAnk1.5 in vitro and in cells.•AnkG107 recruits β-spectrin to a complex of obscurin, sAnk1.5, and AnkG107.•Removing AnkG107's first obscurin-binding domain disrupts obscurin interaction.•AnkG107 obscurin-binding domains do not interact with filamin-C and minimally with plectin-1.