7NIP

titin N2A unique sequence (UN2A) core

Summary for 7NIP

• Entry DOI: 10.2210/pdb7nip/pdb
• NMR Information: BMRB: 50117
• Descriptor: Isoform 11 of Titin (1 entity in total)
• Functional Keywords: titin, n2a, un2a, structural protein
• Biological source: Homo sapiens (Human)
• Total number of polymer chains: 1
• Total formula weight: 4932.73

Authors

Zhou, T.,Kovermann, M.,Fleming, J.R.,Mayans, O. (deposition date: 2021-02-13, release date: 2021-03-03, Last modification date: 2024-06-19)

Primary citation

Zhou, T.,Fleming, J.R.,Lange, S.,Hessel, A.L.,Bogomolovas, J.,Stronczek, C.,Grundei, D.,Ghassemian, M.,Biju, A.,Borgeson, E.,Bullard, B.,Linke, W.A.,Chen, J.,Kovermann, M.,Mayans, O.
Molecular Characterisation of Titin N2A and Its Binding of CARP Reveals a Titin/Actin Cross-linking Mechanism.
J.Mol.Biol., 433:166901-166901, 2021

PubMed Abstract: Striated muscle responds to mechanical overload by rapidly up-regulating the expression of the cardiac ankyrin repeat protein, CARP, which then targets the sarcomere by binding to titin N2A in the I-band region. To date, the role of this interaction in the stress response of muscle remains poorly understood. Here, we characterise the molecular structure of the CARP-receptor site in titin (UN2A) and its binding of CARP. We find that titin UN2A contains a central three-helix bundle fold (ca 45 residues in length) that is joined to N- and C-terminal flanking immunoglobulin domains by long, flexible linkers with partial helical content. CARP binds titin by engaging an α-hairpin in the three-helix fold of UN2A, the C-terminal linker sequence, and the BC loop in Ig81, which jointly form a broad binding interface. Mutagenesis showed that the CARP/N2A association withstands sequence variations in titin N2A and we use this information to evaluate 85 human single nucleotide variants. In addition, actin co-sedimentation, co-transfection in C2C12 cells, proteomics on heart lysates, and the mechanical response of CARP-soaked myofibrils imply that CARP induces the cross-linking of titin and actin myofilaments, thereby increasing myofibril stiffness. We conclude that CARP acts as a regulator of force output in the sarcomere that preserves muscle mechanical performance upon overload stress.

PubMed: 33647290
DOI: 10.1016/j.jmb.2021.166901

Experimental method

SOLUTION NMR