title: Solution structures and dynamics of ADF/cofilins UNC-60A and UNC-60B from Caenorhabditis elegans.
abstract: The nematode Caenorhabditis elegans has two ADF (actin-depolymerizing factor)/cofilin isoforms, UNC-60A and UNC-60B, which are expressed by the unc60 gene by alternative splicing. UNC-60A has higher activity to cause net depolymerization, and to inhibit polymerization, than UNC-60B. UNC-60B, on the other hand, shows much stronger severing activity than UNC-60A. To understand the structural basis of their functional differences, we have determined the solution structures of UNC-60A and UNC-60B proteins and characterized their backbone dynamics. Both UNC-60A and UNC-60B show a conserved ADF/cofilin fold. The G-actin (globular actin)-binding regions of the two proteins are structurally and dynamically conserved. Accordingly, UNC-60A and UNC-60B individually bind to rabbit muscle ADP-G-actin with high affinities, with Kd values of 32.25 nM and 8.62 nM respectively. The primary differences between these strong and weak severing proteins were observed in the orientation and dynamics of the F-actin (filamentous actin)-binding loop (F-loop). In the strong severing activity isoform UNC-60B, the orientation of the F-loop was towards the recently identified F-loop-binding region on F-actin, and the F-loop was relatively more flexible with 14 residues showing motions on a nanosecond-picosecond timescale. In contrast, in the weak severing protein isoform UNC-60A, the orientation of the F-loop was away from the F-loop-binding region and inclined towards its own C-terminal and strand β6. It was also relatively less flexible with only five residues showing motions on a nanosecond-picosecond timescale. These differences in structure and dynamics seem to directly correlate with the differential F-actin site-binding and severing properties of UNC-60A and UNC-60B, and other related ADF/cofilin proteins.
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Vaibhav Kumar
authors.initials: VK
authors.lastname: Shukla
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Ashish
authors.initials: A
authors.lastname: Kabra
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Diva
authors.initials: D
authors.lastname: Maheshwari
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Rahul
authors.initials: R
authors.lastname: Yadav
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Anupam
authors.initials: A
authors.lastname: Jain
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Sarita
authors.initials: S
authors.lastname: Tripathi
authors.affiliation: †Department of Pathology, Emory University, 615 Michael Street, Whitehead Research Building, Room 105N, Atlanta, GA 30322, U.S.A.
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Ono
authors.affiliation: ‡Centre of Biomedical Research (CBMR), Sanjay Gandhi Post-Graduate Institute of Medical Sciences Campus, Raibareli Road, Lucknow 226014, India.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Kumar
authors.affiliation: *Molecular and Structural Biology Division, CSIR-Central Drug Research Institute, Lucknow 226031, India.
authors.forename: Ashish
authors.initials: A
authors.lastname: Arora
mesh_terms: D051339:Actin Depolymerizing Factors / Q000737:chemistry* / Q000378:metabolism; D000199:Actins / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism; D051345:Destrin / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism; D009587:Nitrogen Isotopes; D011485:Protein Binding; D017433:Protein Structure, Secondary; D011817:Rabbits; D017386:Sequence Homology, Amino Acid; D012996:Solutions
chemical_list: D051339:Actin Depolymerizing Factors; D000199:Actins; D000596:Amino Acids; D029742:Caenorhabditis elegans Proteins; D051345:Destrin; D008840:Microfilament Proteins; D009587:Nitrogen Isotopes; D012996:Solutions; C495209:UNC-60 protein, C elegans