Unconventional myosin required during immune response for detection of rare antigen-presenting cells by regulating T-cell migration (PubMed:25083865). Unconventional myosins are actin-based motor molecules with ATPase activity and serve in intracellular movements. Acts as a regulator of T-cell migration by generating membrane tension, enforcing cell-intrinsic meandering search, thereby enhancing detection of rare antigens during lymph-node surveillance, enabling pathogen eradication (PubMed:25083865). Also required in B-cells, where it regulates different membrane/cytoskeleton-dependent processes (PubMed:24310084). Involved in Fc-gamma receptor (Fc-gamma-R) phagocytosis (PubMed:23038771). Interacts with calmodulin; via its IQ motifs. Recruited to Fc-gamma receptor (Fc-gamma-R) phagocytic cup (PubMed:23038771). In T-cells, transiently accumulates in discrete areas at the plasma membrane of migrating cells or when membranes are deformed (PubMed:25083865). Specifically expressed in hematopoietic cells. Detected in adult tissues of the immune system such as thymus, lymph nodes and spleen, but not in brain, lung, heart, liver, small intestine, testis and kidney (at protein level). Highly expressed in T-lymphocytes; constitutes the most highly expressed class I myosin in naive CD4 and CD8 T-cells. Also present in B-lymphocytes. The myosin tail domain mediates binding to phosphatidylinositol-3,4-bisphosphate (PtdIns(3,4)P2), phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) and phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3) and binds to membranous compartments. It is required for recruitment to Fc-gamma receptor (Fc-gamma-R) phagocytic cups. T-cells display impaired migration patterns and are less efficient in scanning and evaluating antigen-presenting cells. T-cells show global reduction in membrane tension, while their homeostatic tissue distribution and responsiveness to T-cell receptor (TCR) engagement are unaffected. However, T-cells move faster and straighter, leading to defects in detection of antigen-presenting cells, specifically for detection of rare antigens. Belongs to the TRAFAC class myosin-kinesin ATPase superfamily. Myosin family. It is uncertain whether Met-1 or Met-7 is the initiator. Represents an unconventional myosin. This protein should not be confused with the conventional myosin-1 (MYH1).