NDP KINASE CAN MODULATE CONTRACTION OF DICTYOSTELIUM CYTOSKELETONS

Extraction of Dictyostelium amoebae with Triton X-100 produces robust cytoskeletons composed mainly of actin and myosin II. These cytoskelet ons rapidly contract when mixed with Mg-ATP in simple buffers. The Tri ton-soluble fraction was found to contain a GTP-dependent activity tha t prevented contraction by Mg-ATP. This activity was purified, and ide ntified as nucleoside diphosphate kinase (NDP kinase). The apparent in hibition resulted from pre-contraction of the cytoskeletons. Tightly b ound cytoskeletal ADP was presumably phosphorylated, and the resulting ATP powered contraction. NDP kinase appeared to be unique in this cap acity, since other regenerating systems did not cause pre-contraction. Reconstitution experiments demonstrated that the kinase must be in ph ysical contact with the cytoskeleton. These results suggest that Dicty ostelium NDP kinase is able to channel ATP to the myosin molecule, and this could play a role in directly regulating cytoskeletal contractio n or in facilitating contraction under conditions where intracellular ATP concentrations are low. This ability to modulate cytoskeletal cont raction could help to explain observations in other systems whereby de fects in NDP kinase result in abnormal development or changes in the m etastatic potential of cancer cells. (C) 1996 Wiley-Liss, Inc.