The type of protein most likely to function as a channel through the plasma membrane is a channel protein. Channel proteins form pores that span the membrane and allow specific molecules or ions to pass through freely, typically by facilitated diffusion, without binding to the molecules or using energy. They often have hydrophobic amino acids facing the membrane interior and hydrophilic amino acids lining the pore to allow passage of polar or charged substances. Examples include ion channels and aquaporins (water channels). Channel proteins can be non-gated (always open) or gated (open in response to stimuli) and enable rapid transport of substances across the membrane.

Carrier proteins, on the other hand, bind their specific substrates and undergo conformational changes to transport molecules, making them different from channel proteins in function and mechanism.

In summary, channel proteins are the class that can function as channels through the plasma membrane.