<p>Model for organisation of ɑ-actinin-2, ZASP and titin Z1Z2 domains in the Z-disc (cardiac myofibrils).</p>

<p><b>A:</b> Arrangement of actin, ɑ-actinin-2, ZASP and titin Z1Z2 in the axial view. The Z-disc in cardiac muscle contains 4-6 ɑ-actinin-2 repeats [<a href="ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1014309#pcbi.1014309.ref005" target="_blank">5</a>], and here 6 repeats are shown. The ɑ-actinin-2 molecules can also be organised into doublets of the homodimer, spaced 6 nm apart ([<a href="ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1014309#pcbi.1014309.ref013" target="_blank">13</a>] not illustrated here for simplicity). <b>B:</b> Arrangement of actin, ɑ‑actinin‑2, ZASP and titin Z1Z2 in the transverse view (basketweave lattice).

The lattice constants for titin Z1Z2 and parallel actin filaments are stable across the Z-disc, while the sets of anti-parallel actin filaments may move relative to one another. The rotation of the square lattice between different locations on the Z-disc is also shown [<a href="ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1014309#pcbi.1014309.ref005" target="_blank">5</a>].</p>