Mutation of Actin Tyr-53 Alters the Conformations of the DNase I-binding Loop and the Nucleotide-binding Cleft

Abstract

All but 11 of the 323 known actin sequences have Tyr at position 53, and the 11 exceptions have the conservative substitution Phe, which raises the following questions. What is the critical role(s) of Tyr-53, and, if it can be replaced by Phe, why has this happened so infrequently? We compared the properties of purified endogenous Dictyostelium actin and mutant constructs with Tyr-53 replaced by Phe, Ala, Glu, Trp, and Leu. The Y53F mutant did not differ significantly from endogenous actin in any of the properties assayed, but the Y53A and Y53E mutants differed substantially; affinity for DNase I was reduced, the rate of nucleotide exchange was increased, the critical concentration for polymerization was increased, filament elongation was inhibited, and polymerized actin was in the form of small oligomers and imperfect filaments. Growth and/or development of cells expressing these actin mutants were also inhibited. The Trp and Leu mutations had lesser but still significant effects on cell phenotype and the biochemical properties of the purified actins. We conclude that either

Structural Differences Explain Diverse Functions of Plasmodium Actins

“…Most of these 11 sequences are actins from Plasmodium or Trypanosoma , both species where actin filaments have not been observed in vivo . Despite the apparent importance of tyrosine at this position for normal actins, a single mutation to phenylalanine in Dictyostelium actin does not affect its polymerization properties [74]. In line with this, we also could not observe long filaments of the actin I F54Y mutant ( Fig.…”

Towards a molecular understanding of the apicomplexan actin motor: on a road to novel targets for malaria remedies?

“…One of the more interesting single residues in this region is Phe53 in actin I, which is a Tyr in almost all other actins. The tyrosine residue is a common phosphorylation site, and mutating it to a phenylalanine in Dictyostelium discoideum actin causes only modest changes in function (Liu et al, 2010), but obviously prevents control by phosphorylation. Phosphorylation of the tyrosine in D. discoideum actin results in a slight stabilization of the D-loop conformation as well as inhibition of nucleotide exchange and decreased filament stability (Liu et al, 2006(Liu et al, , 2010.…”

Oxidative hotspots on actin promote skeletal muscle weakness in rheumatoid arthritis

“…Moreover, H40 and Q41 were located in the so-called DNase-binding loop (D-loop), which comprises residues 38-53 and plays a critical role in longitudinal intersubunit contacts in the filament (30,38) and partakes in the interaction with myosin (39). Consistent with these observations, residue Y53 has previously been shown to be accessible for nitration in vitro by ONOO − (40), and posttranslational modification by phosphorylation of this residue is known to cause slower polymerization and impaired filament stability (41)(42)(43).…”