Pilins are the major structural building blocks of type IV pili. They have a lollipop shape, with a long, hydrophobic N terminal alpha helix and a soluble C terminal domain composed of a beta sheet with the strands connected by loops. They are made as pre-pilins and must have a short leader sequence clipped off the N-terminus before they can assemble into pili.
The pilins assemble in a helical fashion with the hydrophobic N-terminal regions on the inside of the fibre and the hydrophilic C-termini on the outside. The C terminus can be decorated with sugars or other molecules that affect the properties and antigenicity of the pilus. Minor pilins have a similar N-terminus to major pilins, but their C-termini are different. They play a role in pilus assembly, potentially by priming the process.