title: Solution structure and dynamics of ADF from Toxoplasma gondii.
abstract: Toxoplasma gondii ADF (TgADF) belongs to a functional subtype characterized by strong G-actin sequestering activity and low F-actin severing activity. Among the characterized ADF/cofilin proteins, TgADF has the shortest length and is missing a C-terminal helix implicated in F-actin binding. In order to understand its characteristic properties, we have determined the solution structure of TgADF and studied its backbone dynamics from ¹⁵N-relaxation measurements. TgADF has conserved ADF/cofilin fold consisting of a central mixed β-sheet comprised of six β-strands that are partially surrounded by three α-helices and a C-terminal helical turn. The high G-actin sequestering activity of TgADF relies on highly structurally and dynamically optimized interactions between G-actin and G-actin binding surface of TgADF. The equilibrium dissociation constant for TgADF and rabbit muscle G-actin was 23.81 nM, as measured by ITC, which reflects very strong affinity of TgADF and G-actin interactions. The F-actin binding site of TgADF is partially formed, with a shortened F-loop that does not project out of the ellipsoid structure and a C-terminal helical turn in place of the C-terminal helix α4. Yet, it is more rigid than the F-actin binding site of Leishmania donovani cofilin. Experimental observations and structural features do not support the interaction of PIP2 with TgADF, and PIP2 does not affect the interaction of TgADF with G-actin. Overall, this study suggests that conformational flexibility of G-actin binding sites enhances the affinity of TgADF for G-actin, while conformational rigidity of F-actin binding sites of conventional ADF/cofilins is necessary for stable binding to F-actin.
authors.affiliation: Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226001, India.
authors.forename: Rahul
authors.initials: R
authors.lastname: Yadav
authors.forename: Prem Prakash
authors.initials: PP
authors.lastname: Pathak
authors.forename: Vaibhav Kumar
authors.initials: VK
authors.lastname: Shukla
authors.forename: Anupam
authors.initials: A
authors.lastname: Jain
authors.forename: Shubhra
authors.initials: S
authors.lastname: Srivastava
authors.forename: Sarita
authors.initials: S
authors.lastname: Tripathi
authors.forename: S V S R
authors.initials: SV
authors.lastname: Krishna Pulavarti
authors.forename: Simren
authors.initials: S
authors.lastname: Mehta
authors.forename: L David
authors.initials: LD
authors.lastname: Sibley
authors.forename: Ashish
authors.initials: A
authors.lastname: Arora
mesh_terms: D000199:Actins / Q000737:chemistry; D000818:Animals; D002151:Calorimetry; D003198:Computer Simulation; D051345:Destrin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry*; D011817:Rabbits; D040681:Structural Homology, Protein; D013499:Surface Properties; D013816:Thermodynamics; D014122:Toxoplasma
chemical_list: D000199:Actins; D051345:Destrin; D015800:Protozoan Proteins