title: Xin-repeats and nebulin-like repeats bind to F-actin in a similar manner.
abstract: Xin and nebulette are striated muscle-specific actin-binding proteins that both contain multiple actin-binding repeats. The nature of these repeats is different: nebulette has nebulin-like repeats, while Xin contains its own unique repeats. However, the suggestion was made from biochemical data that the Xin-repeats may bind to multiple sites on the actin molecule as was found for nebulin. We have used electron microscopy and the iterative helical real space reconstruction to visualize complexes of F-actin with Xin fragments containing either three or six Xin-repeats, and with the CN5-nebulette fragment, containing five nebulin-like repeats. Our results indicate that Xin and nebulette fragments bind to F-actin in a similar manner and in two distinct modes: in one mode actin subdomain 1 is bound, while in the second mode the binding bridges between a different site on actin subdomains 1/2 of one protomer and subdomains 3/4 of an adjacent actin protomer. Taken together with published data about nebulin, tropomyosin and ADF/cofilin, our results suggest that the ability to bind in multiple modes to the actin protomer is a general property of many actin-binding proteins.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia Health Sciences Center, Charlottesville, VA 22908-0733, USA.
authors.forename: Olga
authors.initials: O
authors.lastname: Cherepanova
authors.forename: Albina
authors.initials: A
authors.lastname: Orlova
authors.forename: Vitold E
authors.initials: VE
authors.lastname: Galkin
authors.forename: Peter F M
authors.initials: PF
authors.lastname: van der Ven
authors.forename: Dieter O
authors.initials: DO
authors.lastname: Fürst
authors.forename: Jian-Ping
authors.initials: JP
authors.lastname: Jin
authors.forename: Edward H
authors.initials: EH
authors.lastname: Egelman
mesh_terms: D000199:Actins / Q000378:metabolism* / Q000648:ultrastructure; D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D002645:Chickens; D018360:Crystallography, X-Ray; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D060588:LIM Domain Proteins; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary / Q000502:physiology; D011817:Rabbits; D020449:Repetitive Sequences, Amino Acid
chemical_list: D000199:Actins; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D004268:DNA-Binding Proteins; D060588:LIM Domain Proteins; D009124:Muscle Proteins; C486890:NEBL protein, human; D009687:Nuclear Proteins; D010446:Peptide Fragments; C500306:XIRP2 protein, human; C035620:nebulin