A coiled-coil domain of melanophilin is essential for Myosin Va recruitment and melanosome transport in melanocytes.
Melanophilin (Mlph) regulates retention of melanosomes at the peripheral actin cytoskeleton of melanocytes, a process essential for normal mammalian pigmentation. Mlph is proposed to be a modular protein binding the melanosome-associated protein Rab27a, Myosin Va (MyoVa), actin, and microtubule end-binding protein (EB1), via distinct N-terminal Rab27a-binding domain (R27BD), medial MyoVa-binding domain (MBD), and C-terminal actin-binding domain (ABD), respectively. We developed a novel melanosome transport assay using a Mlph-null cell line to study formation of the active Rab27a:Mlph:MyoVa complex. Recruitment of MyoVa to melanosomes correlated with rescue of melanosome transport and required intact R27BD together with MBD exon F-binding region (EFBD) and unexpectedly a potential coiled-coil forming sequence within ABD. In vitro binding studies indicate that the coiled-coil region enhances binding of MyoVa by Mlph MBD. Other regions of Mlph reported to interact with MyoVa globular tail, actin, or EB1 are not essential for melanosome transport rescue. The strict correlation between melanosomal MyoVa recruitment and rescue of melanosome distribution suggests that stable interaction with Mlph and MyoVa activation are nondissociable events. Our results highlight the importance of the coiled-coil region together with R27BD and EFBD regions of Mlph in the formation of the active melanosomal Rab27a-Mlph-MyoVa complex.
Hume
Alistair N
AN
Molecular and Cellular Medicine, Division of Biomedical Sciences, Imperial College London, London SW7 2AZ, United Kingdom.
Tarafder
Abul K
AK
Ramalho
José S
JS
Sviderskaya
Elena V
EV
Seabra
Miguel C
MC
D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism*; D002461:Cell Line, Transformed; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008544:Melanocytes / Q000166:cytology / Q000378:metabolism*; D020460:Melanosomes / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018995:Myosin Heavy Chains / Q000378:metabolism*; D024701:Myosin Type V / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021381:Protein Transport
D048868:Adaptor Proteins, Signal Transducing; D000596:Amino Acids; D002352:Carrier Proteins; C435724:Mlph protein, mouse; C513082:Myo5a protein, mouse; D024701:Myosin Type V; D018995:Myosin Heavy Chains