Two major classes of actin-nucleating proteins:

1. Formins nucleate the assembly of unbranched filaments 

2. Arp2/3 complex nucleates the assembly of branched actin networks

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ActA protein binds the host protein VASP, which enhance actin assembly and confine it to the rear of the bacterium.

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Listeria is a food-borne bacterial pathogen has on its surface a protein ActA, which mimics an NPF that efficiently activates the Arp2/3 complex.

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A second NPF is a large protein complex called WAVE

and requires small GTP-binding protein Rac1.

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WASp activation requires two signals (This type of two-signal input, called coincidence detection):

1. regulatory phospholipid PIP2

2. small GTP-binding protein Cdc42

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One NPF is called WASp, as it is defective in patients with Wiskott-Aldrich syndrome.

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The major NPF family is characterized by the presence of a region called WCA (WH2, connector, acidic)