title: Modulation of actin structure and function by phosphorylation of Tyr-53 and profilin binding.
abstract: On starvation, Dictyostelium cells aggregate to form multicellular fruiting bodies containing spores that germinate when transferred to nutrient-rich medium. This developmental cycle correlates with the extent of actin phosphorylation at Tyr-53 (pY53-actin), which is low in vegetative cells but high in viable mature spores. Here we describe high-resolution crystal structures of pY53-actin and unphosphorylated actin in complexes with gelsolin segment 1 and profilin. In the structure of pY53-actin, the phosphate group on Tyr-53 makes hydrogen-bonding interactions with residues of the DNase I-binding loop (D-loop) of actin, resulting in a more stable conformation of the D-loop than in the unphosphorylated structures. A more rigidly folded D-loop may explain some of the previously described properties of pY53-actin, including its increased critical concentration for polymerization, reduced rates of nucleation and pointed end elongation, and weak affinity for DNase I. We show here that phosphorylation of Tyr-53 inhibits subtilisin cleavage of the D-loop and reduces the rate of nucleotide exchange on actin. The structure of profilin-Dictyostelium-actin is strikingly similar to previously determined structures of profilin-beta-actin and profilin-alpha-actin. By comparing this representative set of profilin-actin structures with other structures of actin, we highlight the effects of profilin on the actin conformation. In the profilin-actin complexes, subdomains 1 and 3 of actin close around profilin, producing a 4.7 degrees rotation of the two major domains of actin relative to each other. As a result, the nucleotide cleft becomes moderately more open in the profilin-actin complex, probably explaining the stimulation of nucleotide exchange on actin by profilin.
authors.affiliation: Department of Physiology, 3700 Hamilton Walk, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6085, USA.
authors.forename: Kyuwon
authors.initials: K
authors.lastname: Baek
authors.forename: Xiong
authors.initials: X
authors.lastname: Liu
authors.forename: François
authors.initials: F
authors.lastname: Ferron
authors.forename: Shi
authors.initials: S
authors.lastname: Shu
authors.forename: Edward D
authors.initials: ED
authors.lastname: Korn
authors.forename: Roberto
authors.initials: R
authors.lastname: Dominguez
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D018360:Crystallography, X-Ray; D004023:Dictyostelium / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008958:Models, Molecular; D010766:Phosphorylation; D051304:Profilins / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D014443:Tyrosine / Q000235:genetics / Q000378:metabolism
chemical_list: D000199:Actins; D051304:Profilins; D014443:Tyrosine