Question

You are interested in how intermediate filaments are formed, and you create an intermediate filament subunit whose α-helical region is twice as long as that of a normal intermediate filament by duplicating the normal α-helical region while keeping a globular head at the N-terminus and a globular tail at the C-terminus; you call this subunit IFαd. If you were to assemble intermediate filaments using IFαd as the subunit, which of the following predictions describes the most likely outcome?

1) Filaments assembled using IFαd will interact with different cytoskeletal components.
2) Filaments assembled using IFαd will form dimers that are twice as long as dimers assembled from normal intermediate filaments.
3) Sixteen tetramers assembled from IFαd will be needed for a ropelike structure to form.
4) Dimers of IFαd will form by interactions with the N-terminal globular head and the C-terminal globular tail.

Answer 1

The most probable outcome of using IFαd subunits with doubled α-helical regions to assemble intermediate filaments would be the formation of dimers that are twice as long as normal intermediate filament dimers. The correct option is (4)

Step-by-step explanation:

The student is asking about the likely outcome of assembling intermediate filaments using a hypothetical subunit called IFαd, where the α-helical region is twice as long as that of a normal intermediate filament. In understanding the structure and assembly of intermediate filaments, dimers are the basic building blocks which then aggregate into tetramers and subsequently into higher order structures. The dimers are formed by lateral associations of two monomers via their rod-like coiled-coil domains, followed by a staggered antiparallel alignment into tetramers.

Given the duplication of the α-helical region in IFαd without changing the globular head and tail, the most likely outcome is that these IFαd subunits would form dimers that are twice as long as normal intermediate filament dimers. These elongated dimers may still be able to pair into tetramers, but the overall structure of the intermediate filaments might be altered, potentially affecting the mechanical properties and potentially the interaction with other cytoskeletal components. It is less likely that these subunits would engage in interactions between the N-terminal head and the C-terminal tail within the same dimer, as that is not the typical way that intermediate filament dimers are formed.