Class 2 myosins are a set of protein complexes that bind actin and hydrolyse ATP, acting as molecular motors. They consist of two myosin heavy chains , two essential light chains and two regulatory light chains (MRLCs). Smooth muscle and non-muscle myosin isoforms are a subset of Class 2 myosin complexes. The nomenclature for isoforms is misleading, as non-muscle isoforms can be found in smooth muscle. The 4 smooth muscle isoforms all have heavy chains encoded by MYH11. The non-muscle isoforms have heavy chains encoded by MYH9, MYH10 or MYH14 (NMHC-IIA, B and C). The essential light chain (LC17) common to smooth and non-muscle isoforms is encoded by MYL6. The regulatory light chain (LC20) is encoded by either MYL9, giving a slightly more basic protein that is referred to as the smooth muscle LC20 isoform, and MRLC2, giving a more acidic isoform referred to as the non-muscle LC20 isoform.
Class 2 myosins play a crucial role in a variety of cellular processes, including cell migration, polarity formation, and cytokinesis.