Protein found in or associated with a cell protrusion such as pseudopodium, filopodium, lamellipodium, growth cone, flagellum, acrosome or axon, or bacterial comet tail. These membrane-cytoskeleton-coupled processes are involved in many biological functions, such as cell motility, cancer-cell invasion, endocytosis, phagocytosis, exocytosis, pathogen infection, neurite extension and cytokinesis.
