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.
Department of Biology, University of Tor Vergata Rome, Viale Della Ricerca Scientifica, 00133-Rome, Italy.
Pamela
P
Bielli
Elena Caroli
EC
Casavola
Antonino
A
Biroccio
Andrea
A
Urbani
Antonella
A
Ragnini-Wilson
D020816:Amino Acid Motifs; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism*; D024701:Myosin Type V / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D020761:rab1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D020662:Guanine Nucleotide Exchange Factors; C113979:MLC1 protein, S cerevisiae; C077512:MYO2 protein, S cerevisiae; D018994:Myosin Light Chains; C064456:SEC2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D006160:Guanosine Triphosphate; C087905:YPT31 protein, S cerevisiae; D019204:GTP-Binding Proteins; D024701:Myosin Type V; C121633:YPT32 protein, S cerevisiae; C064320:SEC4 protein, S cerevisiae; D018995:Myosin Heavy Chains; D020691:rab GTP-Binding Proteins; D020761:rab1 GTP-Binding Proteins