GTP drives myosin light chain 1 interaction with the class V myosin Myo2 IQ motifs via a Sec2 RabGEF-mediated pathway.

The yeast myosin light chain 1 (Mlc1p) belongs to a branch of the calmodulin superfamily and is essential for vesicle delivery at the mother-bud neck during cytokinesis due to is ability to bind to the IQ motifs of the class V myosin Myo2p. While calcium binding to calmodulin promotes binding/release ...
from the MyoV IQ motifs, Mlc1p is unable to bind calcium and the mechanism of its interaction with target motifs has not been clarified. The presence of Mlc1p in a complex with the Rab/Ypt Sec4p and with Myo2p suggests a role for Mlc1p in regulating Myo2p cargo binding/release by responding to the activation of Rab/Ypt proteins. Here we show that GTP or GTPgammaS potently stimulate Mlc1p interaction with Myo2p IQ motifs. The C-terminus of the Rab/Ypt GEF Sec2p, but not Sec4p activation, is essential for this interaction. Interestingly, overexpression of constitutively activated Ypt32p, a Rab/Ypt protein that acts upstream of Sec4p, stimulates Mlc1p/Myo2p interaction similarly to GTP although a block of Ypt32 GTP binding does not completely abolish the GTP-mediated Mlc1p/Myo2p interaction. We propose that Mlc1p/Myo2p interaction is stimulated by a signal that requires Sec2p and activation of Ypt32p.
Mesh Terms:
Amino Acid Motifs, GTP-Binding Proteins, Guanine Nucleotide Exchange Factors, Guanosine 5'-O-(3-Thiotriphosphate), Guanosine Triphosphate, Myosin Heavy Chains, Myosin Light Chains, Myosin Type V, Saccharomyces cerevisiae, Saccharomyces cerevisiae Proteins, Signal Transduction, rab GTP-Binding Proteins, rab1 GTP-Binding Proteins
Mol. Microbiol.
Date: Mar. 01, 2006
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