Drosophila ACT88F indirect flight muscle-specific actin is not N-terminally acetylated: a mutation in N-terminal processing affects actin function.
Many eukaryotic proteins are co and post-translationally modified at their N termini by removal of one or two amino acid residues and N(alpha)-acetylation. Actins show two different forms of N-terminal processing dependent on their N-terminal sequence. In class II actins, which include muscle actins, the common primary sequence of Met-Cys-Asp-actin is processed to acetyl-Asp-actin. The functional significance of this in vivo is unknown. We have studied the indirect flight muscle-specific actin, ACT88F, of Drosophila melanogaster. Our results show that ACT88F is N-terminally processed in vivo as a class II actin by removal of the first two amino acid residues (Met and Cys), but that uniquely the N terminus is not acetylated. In addition we show that ACT88F is methylated, probably at His73. Flies carrying the mod(-) mutation fail to complete post-translational processing of ACT88F. We propose that the mod gene product is normally responsible for removing N-acetyl-cysteine from actin. The biological significance of this process is demonstrated by observations that retention of the N-acetyl-cysteine in ACT88F affects the flight muscle function of mod(-) flies. This suggests that the extreme N terminus affects actomyosin interactions in vivo, a proposal we have examined by in vitro motility assays of ACT88F F-actin from mod(-) flies. The mod(-) actin only moves in the presence of methylcellulose, a viscosity-enhancing agent, where it moves at velocities slightly, but significantly, reduced compared to wild-type. These data confirm that N-acetyl-cysteine at the N terminus affects actomyosin interactions, probably by reducing formation of the initial actomyosin collision complex, a process known to involve the actin N terminus.
Schmitz
S
S
Department of Biology, University of York, York, Y010 5YW, UK.
Clayton
J
J
Nongthomba
U
U
Prinz
H
H
Veigel
C
C
Geeves
M
M
Sparrow
J
J
D000107:Acetylation; D000111:Acetylcysteine / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000205:Actomyosin / Q000378:metabolism; D000818:Animals; D004331:Drosophila melanogaster; D015180:Electrophoresis, Gel, Two-Dimensional; D005426:Flight, Animal; D017344:Genes, Insect / Q000235:genetics / Q000502:physiology; D007526:Isoelectric Point; D013058:Mass Spectrometry; D008715:Methionine / Q000378:metabolism; D008745:Methylation; D008747:Methylcellulose / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D014783:Viscosity
D000199:Actins; D020033:Protein Isoforms; C076399:flight muscle protein, Act88F; D008747:Methylcellulose; D000205:Actomyosin; D008715:Methionine; D000111:Acetylcysteine